So, after a few years of being unable to do anything to my site, I'm finally able to update it, which means upgrading to the latest b2evo. However, I'm getting a LOT of errors, mostly "Deprecated" and "Warning: Cannot modify header information - headers already sent by (output started at /home1/dubirdne/public_html/inc/settings/model/_abstractsettings.class.php:121)". I uploaded and overwrote all the b2evo files and still got those errors on the install pages. I did go through the database upgrade part and it said it was done, but I'm still getting them. I tried logging in, and got this error:

Incorrect crumb received! [loginsalt]
Your request was stopped for security reasons.
Incorrect crumb received! Have you waited more than 120 minutes before submitting your request?
Please go back to the previous page and refresh it before submitting the form again.

I did try and reset my password as well, and the link from the email gives a page with this error: "Headers have already been sent in _abstractsettings.class.php on line 121.
Cannot redirect."

I do have a backup of the files and the database so I can roll back, but that doesn't help me in the long run. I'm honestly not sure what to do. I would be ok with stripping and reinstalling, but I have no idea how to do that and keep or migrate the data from the db over so I still have my archive of posts.