Yes, you want size 70/100-17 in the Kenda Tuff tubes. They'll say size 2.25/2.5-17 on the box. I've purchased those for my Symba, and they fit fine.
If you tire is good, then you only need to change out the tube, which only requires taking one side of the tire off of the rim. Before you put the new tube in, though, make sure you check both the inside and outside of tire in case something punctured it. Run a cloth or something along the inside of the tire so anything sharp will catch that instead of your hand.
Changing the tubes and tires takes practice and patience. What's nice about the Symba is that you can work the tire most of the way on by hand, which reduces the risk of pinching the new tube (order an extra tube just in case). Before putting in the new tube, inflate it a little to give it some shape, that will help. A good rule of thumb is to then balance it on your finger - you want enough air so that your finger will rest about halfway up the tube, if that makes sense.
It seems odd to me that your local scooter place wouldn't change the tube at all. If you take them the wheel and the new tube, it should be a pretty easy job for them. Unless, maybe, they don't do tubed tires?