If you mean to upgrade it to a newer version of the iOS, then yes, you sure can. However, you will lose the jail break.
Jail breaks are usually one or two iOS iterations behind. You can have either the freshest iOS or a jail break - not both as a general rule.
Marilyn
P.S. I've taken the liberty and moved this post out of the Polling section over to the Hacking section. Thanks for your understanding.