Before going for a hard reset, it is better to backup your files. for this, you can connect to an external hard disk and copy the important files and photos. in addition, you can sync contacts and calendar events to your Google account also.
steps involved in resetting your phone:
1. Go to setting
2. Scroll down to the end
3. You will see something like "erase all data" or factory reset
4. Click "OK"
The display will go blank, few seconds later you will see it restarting. Now, everything will start from the beginning, as if you are using a new phone.