Hello,

What IPB3 old folders that are no longer used by IPS4 can be deleted?

Is it possible also to do a clean up in the DB after upgrading?

Thanks.

This guide by @Woodsman is nice, and I used it when I upgraded. 

as for the db. make a backup, then make a test install. compare the two db's and delete what's not there.

My way to cleanup "Uploads" folder:

0. Make backup on your HDD! Download "Uploads" folder

1. Create new "storage method" in System - Files - Storage Settings - Configurations. You can create new Directory as example. I use Amazon S3 for it.

2. Change storage method to new for all stuff in "storage settings" (Attachments, ... , Forum Icons, ...)

3. Wait while all necessary files will be move to new destination

4. Delete all non-moved files 

5. Change storage method back again

What about database, maybe some old tables is present after upgrade but they is not so big. Don`t want "broke my head" delete or not  Let it live...