Ok, you've got a few options:
1. Stay on 4.1 and re-jailbreak with limera1n. Limera1n requires a PC/Mac, and learning how to put your phone into DFU mode. Not too difficult, but you may not get it the first few times.
2. Restore to 4.3.3 (more on how to do this in a minute) and use jailbreakme.com to jailbreak. No PC/Mac needed. All you do is open Safari, point your browser to jailbreakme.com, tap the "FREE" button, and in a minute or two, you're jailbroken. Jailbreakme.com only works on 4.3 through 4.3.3.
If I were you, I'd go with option 2. Much easier.
Just curiously, is something wrong with your phone? As Europa stated, unless you really want the few extra features that 4.3.3 has to offer, there's no real reason to update your firmware. My wife is on 4.2.1, and her phone runs just fine. My brother-in-law is still on 4.1 himself.
Restoring to an older firmware requires a little finesse...you have two options here as well:
1. Download the firmware for the model of phone you have (it's an IPSW file), then manually edit the host file of iTunes to point to Cydia's servers (so iTunes is "talking" to it, not Apple's).
2. Use the program TinyUmbrella to trick iTunes for you.
If you want, I can go into more detail on either of these methods, but if there's nothing wrong with your phone, and you aren't dying to try AirPlay or AirPrint, you really don't need to update. Stay where you're at and enjoy your jailbroken iPhone!
Let us know what you decide!