Samsung Galaxy S3 Soft Reset and Hard Reset

If the phone freezes, the most often method is to remove the battery out after a couple of seconds and then putting it back again.

Hard Reset by Code

You can directly reset your device by typing this code *2767*3855#, this will reset your phone automatically once rebooted.

Hard Reset by button combination

Sometimes the code may not always useful specially when your Samsung Galaxy S3 is frozen and become unresponsive or in other sever unresponsive problem like it just stuck on welcome screen logo.
To fix it, just then again remove the battery out, then put it back again. Don't power it ON yet, just press and hold the Volume Up, Center button and Power button at the same time.

A menu will then appear that let choose with an option. Just use the volume button to toggle and select the wipe data/factory reset, that will then reset your Galaxy S III to it's factory default settings.