Disclaimer, this is a guide to help you so use common sense and i take no responsibility if you damage your car.:)

If the mount has gone, you can normally have a rumbling though the car as the clutch pedal is being brought up, as the power from the engine being transmitted to the gearbox and moving the dead bush around more then it should.

If you leave the mount it can and will rest on the exhaust and dent it.
Things that you need;
.Axle stands
.Socket set with a 13mm and 17mm Socket
.13mm and a 17mm spanner
.Crowbar or other item to use for leverage

I would also recommend that you wear overalls, gloves and goggles when under the car.