But you can't restore. Two options to try.
Deleting Cydia Substrate will have the effect of removing all your tweaks (you can reinstall it).
There is also Cydia Impactor which will wipe the phone (all tweaks and data), remove the jailbreak and restore your device to it's current firmware.
But simply restoring won't work. Apple will force you to upgrade to the latest signed version, which depending on your device will be either 8.4.1 or 9.2.1. Both of which are not jailbreakable.
Well, 8.4.1 does have a jailbreak but it's a command line only, proceed with extreme caution type of thing.