Trying to update from 3.4.6 to current

Hello.

We have an old site that hadn’t been updated in a while. Went to update the theme (had to do it manually via FTP) and it broke the site, so had to revert it.

Have tried:

1) Updating via wordpress dashboard…it does not show a new version available (even with API key), however if I upload the new copy of the theme and replace the old one via the themes section of the dashboard, it updates and breaks the site.

2) Manually uploading via ftp. Same thing here, breaks the site.

3) Updating using the Envato helper plugin. Successfully showed that there was an update available, but broke the site anyway.

The site still functions when updated (as in not a fatal php error) , but has a lot missing on the frontend. Things like the footer are gone and certain widgets don’t work. Tried exporting the old theme options before updating, and then importing after updating, just to make sure those didn’t simply need re-set.

Ended up having to update the theme , make my page edits, and then revert the theme. This got the work done that I need right this moment, but we’d still like to be able to update this theme for security and performance reasons.

May we get some assistance with this, please?