how switch to imap on my iphone 4

I have conntacted my supplier and changed the settings on my imac. And I am now trying to sort my iphone 4 to work, I can`t find how to switch from pop to imap. I go into settings-mail contacts-add account ( as i have deleted the orginal)  then I hit other - add mail account- new account and it does not give me any options only pop. I am doing something wrong? Thanks Steve