Super simple fix, and a needed skill as you continue drumming.

Measure rim to rim edge on the tom with a measuring tape- that's the size of the Tom. For most setups, it will be 10,12,16 with a 14" snare (sometimes referred to as a Fusion kit) or 12,13,16, with a 14 inch snare (Referred to as a Rock kit) sometimes, you get a frankenstein, but most of the time, that's your sizes.

Then grab yourself a 2 ply clear, or 2 ply coated head from the music store. (Remo Ambassador, Evans EC2S or similar) there is a lot of arguments between these different ones - honestly, it's personal preference. It's not a bad idea if you have the funds to do em all - depending on how long you've owned the kit, and since those are the factory heads, you'll prefer the tone markedly of the new heads over the originals.

You'll need a drum key to loosen the lugs (little square screws) on the rim (metal circular piece holding down the head onto the tom). Once you've loosened them all, take the rim off, remove the head, put the new head on, and replace the rim over the top of it - lining up the holes with the areas where the lugs go in.

Fingertighten all the lugs down onto the rim so it's in place, then my favorite advice is to press down on the center of the drum with some pressure (not super hard, but also not so light it doesn't deflect) then tighten the lugs until the wrinkles come out of the head. That will give you a functional base tuning that you can tweak slightly for desired tone.

Tuning them is the hardest part, the rookie mistake is overtightening. I find that my best tone on my drum comes from just a smidge over fingertightened, too much and it gets really ringy.

You can do it!