Once you have root access you'll need to install a custom ROM. I'm not sure if there is a Jelly Bean ROM available, so search this forum and see what is available. Remember to read up on installing ROMs so you understand how to do it and not brick your device.
I know of no work that's been done or is in the works for a Jellybean ROM. I'm not sure the Revo's 512 MB of RAM could effectively deal with Jellybean.
Jelly Bean may never be made for the Revolution, But with Kit-Kat there may be a chance if someone wants to work on it. Kit-Kat is designed to run on new phones as well as older 512Mb phones.