Will this 3.8/4.0 swap work? How should I?

[JohnnieOO]

I've been putting off upgrading from 3.8.7 to 4+, well, today I'm unexplainably getting SQL errors on the website (but none found on the backend) and I have been unable to diagnose. So, I guess I'll go ahead and jump to 4. Originally, my 3.8 VB is in website.com/forum with vbadvanced CMPS in the home directory. Due to the errors I'm having, I cannot get to the existing VB/AdminCP to execute any diagnostics.

Is there a simple method to swap 3.8 to 4.0? Do I need to reinstall 3.8 and upgrade? Can I just delete 3.8 and install the 4.0 files in the "forum" directory (and keep the config settings)? If I delete the "forum" directory and install a clean 3.8 in a new "forum" directory, will the mods come with the unaltered database? I am not experienced enough to KNOW what to do here. I seem to understand that the mods are in the database, right?

Long story short, I want to keep all of my posts, users, threads, etc...but I want to avoid the errors I am experiencing.

Thanks,
Johnnie