Small Engines (Lawn Mowers, etc.): hard to shift, series model, model numbers

Question
I have a Sears T-1000 riding lawn mower.  It is almost impossible to shift gears.  When I depress the clutch/brake pedal, the lawnmower doesn't stop.  It just keeps going like it is in neutral.  Depressing the pedal doesn't make it any easier to shift either.  Could the clutch be out of adjustment, and if so, how do I adjust?

Answer
Hello Richard:

There are Severa Possible Causes for this. However, the Numbers you Sent me are the Series Model. Send me the Model Numbers Off the Mower, Please. With these I can Locate the Proper Manual and Better Assist you. They are the XXX.XXXXXX Numbers I Require. The are Usually Under the Seat on the Seat or the Frame. Thanks.

Respectfully

John