If you are asking how to do a "Hard Reset", I will include the instructions below. However, before doing so (as it will wipe all your data on the device) you might want to try and see if you can run antivirus (or two) on it first. So you will have the opportunity to get your data off of it before the reset.
NOTE: Doing this will clear 'all' the data on your phone, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the phone.
Be sure you back up any data you want to keep, to a computer or cloud account, before doing the reset.
To "Hard Reset" the phone...
1. Make sure that the phone is actually powered off.
2. Remove your SD card, if there is one in the device.
3. Press...