Update Jailbroken iphone 4.2.1 - ios5

[les11068125]

How do I go about updating my iPhone 3gs its on 4.2.1 the jailbreak was not used to unlock the phone, I dont wish to keep any apps that I had, I just want to upgrade to ios5, but im worried that i will break it by clicking on update in itunes.
also the power/sleep button is not working will this be a problem?

 

[Doba]

Do you rely on unlock? If not, just plug it into iTunes and update. You will not be able to enter DFU mode and jailbreak it without the power button.

 

[les11068125]

no i dont rely on unlock. So i just have to click update? and in doing so it wont break the phone eg brick it or black screen or anything?