how can i tell if my skin will pass the upgrade?

[nbaphenom]

How will I know it doesn't mess up any way ?

[RLShare]

Use a testboard that is an exact replica of your forum, upgrade the testboard and review the 'outdated templates' notification that will appear when you first log into your adminCP.

[nbaphenom]

So just install a new vbulletin in a directory upload the skin and upgrade it?

[Dismounted]

You are allowed one test board according to the vBulletin License Agreement. The LA states that it must be placed in a directory called "testvb" and must be password protected so that the general public cannot see the board.