From rebug 4.21 to 4.50 ita?

Hello everyone. I made the cex to dexx tutorial, and im on rebug 4.21(Dex), and i want to go to 4.50ita. How can i do it?
A friend told me that i need to go to 3.55dex or something like that, but i dont know how :P
Can someone help me please?
Thanks!
(Sorry 4 bad english. Not my main language)