Can't update software on Thunderbolt

[Dukemost]

So I just go a Thunderbolt from my friend for free to use for internet, games and mp3 player it has a bad ESN but its okay I don't plan on connecting it to Verizon. The problem is that I want to do a software update but every time I try it doesn't let me. Right now its at 2.3.4 Android Version and would love to have it up to date. Is there any way to update it? Thanks for you help.