What's the best way to upgrade my forum and only keep members?

Delete all photos, files and whatsoever and start clean on 4.0

All forums will also have to be created again, how would I do this? I'm going to use my old memberbase on a new forum.

Upgrade and then delete everything you don't want. There is not really a selection process of "what to keep" in the upgrade process so anything like this you are going to be on your own to manually perform.

Upgrade and then delete everything you don't want.

​I'd actually suggest delete what you don't want prior to the upgrade - less to deal with after the upgrade (rebuilding/reindexing)

Delete the contents of forums -> you've got an "Empty Forum" option in forum management to do this.

Delete any existing forums on the board -> you've got a "Delete Forum" option to do so.

​I'd actually suggest delete what you don't want prior to the upgrade - less to deal with after the upgrade (rebuilding/reindexing)

Delete the contents of forums -> you've got an "Empty Forum" option in forum management to do this.

Delete any existing forums on the board -> you've got a "Delete Forum" option to do so.

​I guess.

What should I do about all the applications and stuff, can i just make a new folder and install it there then it will automaticly upgrade once i apply db details or do i manually need to clean up the files and apps