Updating from version 3.0.2

Hello,
I have just come back to managing a site I built 8 years ago and the WP core, PHP version and, GP theme haven’t been updated in a long time, I tried updating everything and the site would break. I managed to upgrade WP from 5.5 to 6.0 and GP 3.0.2 is still working (PHP at 7.4). STEP 1: I want to upgrade GP to a more recent version and then STEP2: upgrade it to 3.6 after so I can enventually upgrade to WP 6.8.

What would be the best version of GP to use in step 1? I need a GP version that will work with WP 6.0 to 6.5 – I think that GP 3.6 works with WP 6.5??

Also, what is the easiest way to install a newer version of GP that isn’t the latest release?

Thanks in advance for your help

The page I need help with: [log in to see the link]