The technical last jailbreak for the iPhone 4 is on iOS 7.0.2 with OpenSn0w, which is NOT for average users. Sure you can jailbreak your device yourself using OpenSn0w by all means, but unless you know exactly what you're doing, you won't be able to use it since it's a jailbreak down the very raw. In addition, there are little to no support for the 99%+ packages in Cydia. Themes can work, but you have to manually implement them because Substrate is not fully tested and hoisted online for public access as is an updated version of Cydia
And contrary to what the above user said, ILEX RAT nor Semirestore allows you to keep your Cydia tweaks unless you're strictly removing all the tweak settings, which will have no affect at all on any pre-existing issues you're trying to resolve. The best way to get it all fixed and working again, is to backup your device completely using iTunes, then backing up all your packages and sources using tweaks like PKGBackup, xBackup and those alike, backup that archived backup of packages and sources, then use ILEX RAT via MobileTerminal/SSH Command/Terminal Command to wipe your device completely. Restore the backup, open up Cydia, re-install the tweak you installed earlier to backup your packages and sources, port the backed up archive from earlier back onto your device, and extract it.
Depending on the number of tweaks you have, it can take anywhere from 5 minutes to an hour to get done.