How do I change my email?

On the right side bar, under the MEMBERS tab, click on User CP. Then you'd be redirected to the user control panel. Under the "My Control Panel", there is an icon of like 3 people with "Edit profile". Click that and you'd be redirect again to "Change my info" where you can change your email/password/avatar/etc. Once you change it, you should scroll down and click the update info.

Condensed version:
User CP>Edit profile

Oh, I have a question regarding this too: I've tried to change my email but it says that my new email was already in use. I don't think I've ever used the new email for this site(I checked my old emails + spam for confirmation emails) but it still won't let me use my new email. And since there's no option to send an email for forgotten passwords without knowing the username, I'm kind of stuck here.

Message me about your other email, and I can check if there's another account under it

A just ruler amongst tyrants