Okay, i'll answer your questions one at a time.
Originally posted by another user
1- If im on Rebug 4.46 D-REX and i want to update to 4.50ITA, i need to downgrade to DEX 3.55 than go to 4.50ITA or i can go straight from Rebug 4.46 D-REX To 4.50ita?
From 4.46 D-REX you can lay the 4.50 ITA File right on top of that. You don't have to downgrade to transfer through these firmwares.
Originally posted by another user
2- if im on 4.50ITA abd i want to go to Rebug 4.45 D-REX, i need to downgrade to DEX 3.55 than go to Rebug 4.46 D-REXor i can go straight from 4.50ITA to Rebug 4.46 D-REX?
However, if you are going backwards you need to downgrade to 3.55 and install your Rebug 4.46 again.