Hi.
You should backup your data first, such as pictures, whatsappp messages and app/game data which can be backed up via google drive or play games.
I would advise to move pics to your pc, to backup your contacts you should go into you contact list and clicly the 3 dots or by long pressing the left virtual button (i do not know what os version are you on) to navigate to something saying import/export contacts and to export contacts in the .vcf file type and transfer that into your pc.
After you backed up your data remove any lock pins and then turn off the device, press the home button and then volume up and keep them pressed and press the power button, keep all the 3 buttons pressed till you are into recovery mode.
At that point perform the factory wipe (hard reset) option which will erase all you data and you will havo to SET UP AGAIN ALL THE PHONE like when you bought it (NB ALL NON BACKED DATA WILL BE LOST).
By doing so you should solve software problems which came up spontaneosly.
Let me know
