how to upgrade a Add-ons from 3.8 to 4.x
 

how can i upgrade Add-ons from 3.8 version to 4.x.x ?

Most of the changes have to do with template rendering and preregistering your variables for use in the templates. Cellarius wrote a really good article that you may be interested in - [vB4] Rendering templates and registering variables - a short guide I'd also suggest downloading a couple modifications that were made for 3.x and upgraded to 4.x and comparing them to see what was done.

Hm. I think I'm reading your question differently than Lynne.

Usually you just have to do some searches for a vb4 version of the 3.8 mod you're using. Many have vb4 versions, some don't. Once you find one, read it's entire thread to learn about possible complications, then read the upgrade instructions very carefully, and follow them.