There shouldn't be any problem at all. Just click add new account, and follow the onscreen directions. In fact, I doubt if you have to delete your POP account first, but if you don't, it might make it more confusing for you. Try it on your iPhone first, if you just add imap and don't delete your pop, it will just show up as a separate account, so no harm, no foul, so to speak.😉
Before you add it to your iPhone, it would probably be helpful if you open your mail settings, click on your account, and on the first page that comes up, the very first setting at the top allows you to turn that account off. Just set it to off, that will disable the account without deleting anything. Then you can decide which account you like and delete the other one. Just be aware that for it to work properly, you need to have imap set up on all devices, not just the phone. You can also disable your POP account in outlook and add Imap there, without deleting anything.