Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
ok - you'll definitely need to backup or move the 70GB - if you sign out of onedrive from that account, the locally cached files will be saved on the hard drive. just make sure you have everything synced in full before you cancel the account - it should stay accessible for at least a few days, but i'd take the safe route and make sure everything is downloaded before you cancel it.
Oh, and export your mailbox to a pst. As long as the address isn't being moved to a new tenant, you can leave it in the profile, but the password dialog gets annoying.
Add the new account to onedrive. Set up the email account in outlook.
Remove the computer from the first account installation list (remove all computers and cancel the subscription if that is the plan). When office deactivates, use the new address to activate it.