What can I do to make an older Lowes brand garden tractor go faster?

So, the mower is about 10 or 12 years old, and its an older lowes brand mowerI have removed the deck, and it is basically a toy. All it has to do is drive. (And also all it currenly does). What can I do to make it go faster? (WITHOUT investing more than about 15–2 dollars). Any suggestions?
(It currently has an 11hp motor and only goes a few miles an hour. If i could get it up to about 10 mph at top speed, that would be great!)