My ex-boyfriend set up my Roku Express, I'm assuming with his email/password. I have my own roku account and I want to connect that roku express I have to my account to change the name. How do I put my Roku Express on my account when it's already on another account?
You have to perform a factory reset and go through the setup process again to link to a different account. You can factory reset from Settings->System->Advanced system settings. Keep in mind there is no fee to activate a Roku and if there's a code displayed on your TV screen while setting it up make sure you go to https://my.roku.com/link. Roku is switching to an email activation, so you may or may not get the code activation method.
If I factory reset, won't all my apps be wiped out then I have to re-download them and login?
The apps are based one whatever account the Roku is attached to so that was going to happen either way. Just make a note of them. The channel store is probably the quickest way to add a bunch of channels:
https://channelstore.roku.com/browse
For any premium channels that need logging in (and paying), you'll need to take care of that.