Your code isn't exactly clear. You posted your button click code but it looks like you are deciding if it is the save button and if not it is the update button.
if (Btnsave.Text == "Save")
{
Then you've got a row command, which i don't know what that is, but this looks like where your delete logic is as i see a check for EDT (assuming Edit based on stored proc name) otherwise it is the delete command
if (e.CommandName == "EDT")
{
So with that said, i'll answer this questions with two possibilities.
1) Inside your row command code you've got a call to usp_Registration_Delete. Inside this IF statement is where you should perform your delete operation. Since i don't have access to your computer/code I'm having to make many assumptions. But in your EDT if block, you've got this line
ViewState["Files"] = ds.Tables[0].Rows[0]["Files"].ToString();
If that is the filename you wish to delete. The inside the DLT if block is where you would delete the file.
else if (e.CommandName == "DLT")
{
var fileToDelete = ds.Tables[0].Rows[0]["Files"].ToString();
con.Open();
SqlCommand cmd = new SqlCommand("usp_Registration_Delete",con);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("@RID",e.CommandArgument);
cmd.ExecuteNonQuery();
con.Close();
File.Delete(fileToDelete);
Fill_Grid();
}
2) If the first block of code you posted is the sole button click, then you need to add another if statement to determine if it is delete vs save vs delete
Basically
if (Btnsave.Text == "Save")
{
}
else if (Btnsave.Text == "Update")
{
}
else if (Btnsave.Text == "Delete")
{
}
If this is what needs to happen, then you just take the code from option 1) i posted above, place it inside the Btnsave.Text == "Delete" if block, and then delete the file using the FN variable you posted above (assuming thats the file to delete).
FN = Path.GetFileName(fufile.PostedFile.FileName);
File.Delete(FN);
If none of this steers you in the right direction, i would encourage you to use Improve Question link on your initial post to add more details and information to get the assistance you are looking for.