Find out how to prepare to iOS 7 update without loosing jailbreak. You can wait or until iOS 7 jailbreak release or you have SHSH blobs saved which you can use to downgrade the new firmware to jailbreakble version.
Read really needed info for iOS users brought to you by iH8sn0w (Snowbreeze, iFaith, etc. developer):
I'm an iPhone 4 user, what should I do? If you have not already, make sure you save your iOS 6.1.3 SHSH blobs with iFaith, TinyUmbrella, or redsn0w (ipsw required). There is a lot of confusion about having to be running iOS 6.1.3 to obtain such blobs. No, that requirement only applies if you're dumping blobs right off the device. Which also makes me mention, if you have a firmware below 6.1.3 and do not have SHSH blobs for it, make sure to grab those blobs with iFaith. If you obtain these SHSH blobs, you are free to upgrade to iOS 7 and downgrade back down in case of anything getting released (DOES NOT APPLY TO A5 USERS). I'm using a device with an A5 processor or higher, what should I do? If you are currently on iOS 7, I would recommend downgrading to 6.1.3/6.1.4 (via DFU). Why? There is currently a possibility of a potential 6.1.3/6.1.4 untethered A5+ jailbreak being pushed in the upcoming days/weeks. If you wish to be included if such thing takes place, downgrade now. While you still can! Once iOS 7 goes live later today, the 6.1.3/6.1.4 signing window should close within the hour of the release (possibly even minutes). If you're still running 6.1.3/6.1.4, today is your last chance to restore and get a "fresh" start. If you're jailbroken on 6.0 --> 6.1.2 with evasi0n, you're better off staying where you are. It is worth staying on 6.1.3/6.1.4 while iOS 7 is out if you want the chance to jump on board the potential A5+ 6.1.3/6.1.4 jailbreak. Once an iOS 7 jailbreak goes public, then you should have no concerns about the upgrade. Also, although many people find it "useless" to save A5+ SHSH blobs, you're not going to lose anything by connecting your device and clicking a button. The saying is "Better safe, then sorry!". If some sort of low level boot loader exploit or apticket loophole goes public, such A5+ SHSH blobs will become useful again. (It is also worth noting that it is currently useless to look into 6.0 --> 6.1.2 A5+ downgrading due to Cydia caching incomplete aptickets.). As usual, you can save A5+ shsh blobs for 6.1.3/6.1.4 by using either iFaith (click Show available caches on server and follow prompts), TinyUmbrella, or redsn0w (ipsw required).
Source: iH8sn0w blog