How do i change both tires since they are both sitting on their rims?

if the car is on a hard surface, like your driveway, the only safe method is to borrow a floor jack (like a shop would use) then put metal jack stands on both ends of the car.

You want to place your jack stand in the middle of the car, on that side, preferably on the frame but if that's not possible, use the very edge where there is a lip.

Youch. This is a great chance to have her buy you a 2 1/2 Ton floor jack ($50-$70) and 4 legged jack stands ($20-$25). These are great. You can jack up the car from a center cross member and lift the whole front or back of the car at once. You can get them at Sears, WalMart, Target or NAPA. I'd recommend one with fat, sturdy-looking wheels that won't sink in to asphalt. They have 3-legged jack stands, but I suggest the 4-legged kind for stability. PS: I got my jack stands at Target for like $15 on sale.