i already have a account set up on eM Client with imap, how to do i change to the account to pop3 or add smtp to allow sending email ?

You can’t change the protocol to POP3, you will have to set up the account again.  When you add the account, do not use the automatic setup, but choose Mail and click on the Other icon.  You will need to st up SMTP at the same time, as you can’t add it later.