Knowledge base for upgrading to 4.0 from heavy modified 3.8

[محروم.كوم]

Hi,

I would like to know (at least evaluate) how much time and how it will be hard (or not) for me to upgrade some of my heavy modified vb 3.8 boards to vb4.0 series.

(Not kidding about heavy, it's really heavy.)

In my member account I only see 3.8 manual and I don't find on vb.org any "how to" detailed on this subject.
Is there any tutorial or documentation for upgrading deep personal custom mods available without buying a new 4.0 licence ?
Is there at least semi-public knowledge base about 4.0 (manual) for 3.8 licence owner ?

Sorry if question was already asked. __DEFINE_LIKE_SHARE__