Soft reset is level one, it restarts your phone. How to do it is hold down the Volume Down and Power Buttons at the same time for 10 seconds.
Hard reset is level two, it restarts and erases your data (personal and app). You can do this by going into settings, about, "reset your phone."
Factory reset is level three, it resets your phone back to factory settings.
Power down your phone and then do the following :
Press and hold the power key until the phone vibrates then release
Press and hold the down volume key. An exclamation mark will be shown, then you can release.
Input the following key combination : Volume Up -> Volume Down -> Power -> Volume Down
Your phone will then restart and boot up automatically.
All this information was found on these forums, and a quick search
would have given you the same information, but hope this helps!