I have a new email address and need to delete old primary email so I can access Apple Apps

My email address on my iCloud account is old and not useable. However, I can’t seem to change it and am worried what will happen if I delete and start again. My goal is to share documents among my phone, iPad and desktop Windows. I have Windows 365 and am paying a monthly fee for that as well as a monthly fee for iCloud and yet I’m not synced up to use them properly.

Change your Apple ID - Apple Support

I have a new email I want to replace my Apple ID (which is my old email) with it. I am afraid to delete it and type the new one in.