This is a easy methode to disable the software updates in IOS. If you disable the Software updates, you wont be able to see the option in the settings app anymore, and you dont get notifications from any IOS updates.
First of all go to Cydia and click sources. Then add this repo : http://cydia.angelxwind.net/ After that you need to search for the tweak called ''Mikoto''. Install that tweak on your IDevice. After the respring go to settings and search for ''Mikoto'' Then click on Mikoto and you'll see a option called settings open that. Then enable the option ''Software update disabler''.
If you want the updates back again just disable the option.
Now you wont see any updates or get notifications from IOS updates. So you wont lose your jailbreak anymore.