How can update my CFW 3.55 version to CFW 4.xx

Hello to every one,
I have been using PS3 3.55 CFW for about 4 years with the same fw installed. I don't know which cfw version it is because I couldn't install it myself.
I reviewed the current cfw on the site. Can I upgrade my version by installing these versions on my ps3?
Which of the dex or cex versions should I install?
and which version should I use?