this is my stored procedure for insert. how to write the same for update.

You need to identify a primary key set for your table before you run an update - it could be firstname, lastname combination or even a new unique primary key identity.

You can then easily update based on this key.

E.g.

Update primaryskill=@primaryskill, secondaryskill=@secondaryskill...
where firstname = @firstname and lastname=@lastname

Few things and Steps:
1. Post insert, there must be some primary key that would represent the inserted record uniquely.
2. For an Update, this KEY would be the one used to find the record and update.
3. Comparing to above, the difference would be:
a. add additional unique id parameter
b. change INSERT query to an UPDATE

Thus, it would be something like:

UPDATE 
   Resources
SET
   FirstName = 'Sandeep', 
   LastName = 'Mewara'
WHERE
   UniqueIdColumnName = @UniqueIDAsPrimaryKey

Try out! See if you face any issues.

CREATE PROCEDURE [dbo].[spUpdateResource] @FirstName VARCHAR(50),
    @LastName VARCHAR(50),
    @PrimarySkill VARCHAR(50),
    @SecondarySkill VARCHAR(50),
    @Email VARCHAR(50),
    @Phone INT = 0,
    @ResourceManager VARCHAR(50),
    @Customer VARCHAR(50),
    @StartDate DATETIME,
    @CompanyName VARCHAR(50),
    @ContactLastName VARCHAR(50),
    @ContactFirstName VARCHAR(50),
    @Duns VARCHAR(50),
    @PayRate VARCHAR(50),
    @citizen VARCHAR(50),
    @GC VARCHAR(50),
    @EndDate DATETIME,
    @CustomerManager VARCHAR(50),
    @CreatedAt VARCHAR(50),
    @CanadianCitizen VARCHAR(50),
    @ReferenceName1 VARCHAR(50),
    @ReferenceName2 VARCHAR(50),
    @Email1 VARCHAR(50),
    @Email2 VARCHAR(50)
AS
BEGIN
    UPDATE Resource
    SET FirstName = @FirstName,
        LastName = @LastName,
        PrimarySkill = @PrimarySkill,
        SecondarySkill = @SecondarySkill,
        Email = @Email,
        Phone = @Phone,
        ResourceManager = @ResourceManager,
        Customer = @Customer,
        StartDate = @StartDate,
        CompanyName = @CompanyName,
        ContactLastName = @ContactLastName,
        ContactFirstName = @ContactFirstName,
        Duns = @Duns,
        PayRate = @PayRate,
        citizen = @citizen,
        GC = @GC,
        CanadianCitizen = @CanadianCitizen,
        EndDate = @EndDate,
        CustomerManager = @CustomerManager,
        CreatedAt = @CreatedAt,
        ReferenceName1 = @ReferenceName1,
        ReferenceName2 = @ReferenceName2,
        Email1 = @Email1,
        Email = @Email2 
     WHERE Email = @Email AND Email1 = @Email1
    SELECT *
    FROM Resource
END

Hope this helps
--RDBurmon

try below:

ALTER PROCEDURE [dbo].[Resource_sp] 
    @FirstName varchar(50),
    @LastName varchar(50),
    @PrimarySkill varchar(50),
    @SecondarySkill varchar(50),
    @Email varchar(50),
    @Phone int=0,
    @ResourceManager varchar(50),
    @Customer varchar(50),
    @StartDate DateTime,
    @CompanyName varchar(50),
    @ContactLastName varchar(50),
    @ContactFirstName varchar(50),
    @Duns varchar(50),
    @PayRate varchar(50),
    @citizen varchar(50),
    @GC varchar(50),
    @EndDate DateTime,
    @CustomerManager varchar(50),
    @CreatedAt varchar(50),
    @CanadianCitizen varchar(50),
    @ReferenceName1 varchar(50),
    @ReferenceName2 varchar(50),
    @Email1 varchar(50),
    @Email2 varchar(50),
    @Flag varchar(10) 
    
    AS
    BEGIN
    if @Flag = 'INSERT' 
      Begin  
    	Insert into  Resource(FirstName,LastName,PrimarySkill,SecondarySkill,Email,Phone,ResourceManager,Customer,StartDate,CompanyName,ContactLastName,ContactFirstName,Duns,PayRate,citizen,GC,CanadianCitizen,EndDate,CustomerManager,CreatedAt,ReferenceName1,ReferenceName2,Email1,Email2) values (@FirstName,@LastName,@PrimarySkill,@SecondarySkill,@Email,@Phone,@ResourceManager,@Customer,@StartDate,@CompanyName,@ContactLastName,@ContactFirstName,@Duns,@PayRate,@citizen,@GC,@CanadianCitizen,@EndDate,@CustomerManager,@CreatedAt,@ReferenceName1,@ReferenceName2,@Email1,@Email2)
     end
    if  @Flag = 'UPDATE' 
      begin
          Update Resource set FirstName = @FirstName,
                             LastName = @LastName,
                            PrimarySkill = @PrimarySkill,
                            SecondarySkill = @SecondarySkill,
                            Email =@Email,
                            Phone = @Phone,
                            ResourceManager = @ResourceManager,
                            Customer = @Customer,
                            StartDate = @StartDate ,
                            CompanyName  =@CompanyName,
                            ContactLastName = @ContactLastName,
                            ContactFirstName = @ContactFirstName,
                            Duns = @Duns,
                            PayRate = @PayRate,
                            citizen = @citizen,
                            GC = @GC,
                            CanadianCitizen = @CanadianCitizen,
                            EndDate = @EndDate,
                            CustomerManager = @CustomerManager,
                            CreatedAt = @CreatedAt,
                            ReferenceName1 =@ReferenceName1,
                            ReferenceName2 = @ReferenceName2,
                            Email1 = @Email1,
                            Email2 = @Email2  
              WHERE    //your Condition with primary key of DataBase table
      end 

    SELECT * from Resource
     
    END