Disengage the clutch lever and then remove the mowing deck. Immediately afterwards, your next challenge is pulling off the drive belt which is situated on the engine pulley. You'll then need to remove a total of three retainer springs of varying sizes before removing the belt collar entirely.
Then, remove the anti-sway bar rods, cotter pins, front links and the suspension arms, which should now be in an upward direction. This allows you to remove the mower deck in full, in addition to taking the drive belt off the two remaining pulleys. After this, the only thing that remains from you removing the drive belt on your Murray Rider mower is the trans axle pulley. Once it is completely detached, you need to get the new drive belt and reassemble everything in reverse order, working your way from the bottom of this answer right up to the top. There you go: A good-as-new Murray Rider mower!