How to use not equal to in join

This is the script of my tables


Create Table IM 
	(
		ID int idenetity (1,1)
		,Code varchar(100)
		,CurrentMrp float
		,CurrentCP float
		,lastMrp float
		,lastCp float
		, effective_st_dt date
		,effective_end_dt date
	)

Create table IME
	(
		Code varchar(100)
		,CurrentMrp float
		,CurrentCP float
		,Effective_st_dt date
		,Effective_end_dt date
	)

insert into IM (code,currentMrp,currentCp,lastMRP,lastCP,effective_st_dt,effective_end_dt)
	Select 'CA123',10.12,5.0,8.20,4,'2014-05-01','2014-05-31'
union
	Select 'CA123',15.0,5.0,10.12,8.20,'2014-06-01','2014-08-31'
union
	Select 'CA121',50.0,15.0,45.0,25.0,'2014-04-01','2014-05-31'
union
	Select 'CA121',75.0,25.0,50.0,15.0,'2014-06-01','2014-06-30'
union
	Select 'CA131',53.0,12.0,35.0,10.0,'2014-05-01','2014-05-31'
union
	Select 'CA131',60.0,15.0,53.0,12.0,'2014-06-01','2014-08-31'


Insert into IME (code,effective_st_dt,effective_end_dt)
	Select ('CA123',20.0,5.0,'2014-06-01','2014-08-31')
union
	Select ('CA123',25.0,6.0,'2014-06-20','2014-08-31')
union
	Select ('CA123',35.0,7.0,'2014-07-15','2015-03-31')
	

I have 3 scenarios to implment.

Case 1- When IM.Code=IME.Code and IM.Effective_st_dt=IME.effective_st_dt and IM.Effective_end_dt =IME.Effective-end_date

Action- 
In this case i need to update the IM with currentMrp and currentCp.

Case 2- When IM.Code=IME.Code and IM.Effective_st_dt!=IME.effective_st_dt and IM.Effective_end_dt =IME.Effective-end_date

Action- 
1.)Pick the recent Effective_st_dt record from IM and Update the Effective_end_date with (IME.Effective_st_dt)-1

2.)then Insert a new record from IME which has new effective_st_dt also this record lastMRP and lastcp is the currentmrp and Currentcp of the previous record which is updated in 1

Case 3- When IM.Code=IME.Code and IM.Effective_st_dt!=IME.effective_st_dt and IM.Effective_end_dt !=IME.Effective-end_date

Action-
1.)Pick the recent Effective_st_dt record from IM and Update the Effective_end_date with (IME.Effective_st_dt)-1

2.)then Insert a new record from IME which has new effective_st_dt also this record lastMRP and lastcp is the currentmrp and Currentcp of the previous record which is updated in 1