Its a manual transmission with 4 gears and reverse.
But when I am trying to switch between gears I have to hit the shifter with my foot quite a few times. any suggestions?

 

I have noticed that after riding it a little bit, shifting becomes easier, but still not as easy as it should be.
Ill be riding it in 4th and come up to a turn, but wont be able to downshift to take the turn, so I end up stopping and messing with the shifter with my hand to get it to go down to 3rd, 2nd, and 1st. Its a real hassle not knowing if your bike is going to cooperate on a trail or not. any input would be appreciated.

 

it would be no harm checking the oil to see what colour it is.. if it is silver or you can feel grit when you rub it in between your figures its a good sign that the gears are really worn. there is a possibility an oil change could help in getting rid of the shavings and make it easier for you!!

here is a small bit of advice for all engines, if you place a decently strong magnet on the oil drainage bolt as the gears wear down the filings will be pulled down to the bolt out of the way of the gears!!! and when you change the oil you can easily scrape off the filings!! just helps in keeping everything healthy

 

I will give the oil a try. What type of oil should I be using? I bought this quad used on craigslist, and have no idea what type to use.

 

well that depends on your climate... if its hot around you then lawnmower oil (30w) would do but in winter it is way too thick!! here in ireland i just use car oil because it works at both extremes of temperatures!!! but im not pretending to be any sort of expert but i have had no problem at all with the synthetic car engine oil

 

I drained the old oil and it was full of metal shavings and looked like it was really past due for an oil change, but so far the shifting problem hasn't went away since i changed the oil

 

You may have damage inside the cases or you may just have a bent/worn shift fork.. The shift fork is under the clutch assy under the right side case(when sitting on the quad).. Id guess the shift fork is worn and not spinning the shift drum enough.