There are many ways to remove a tyre off a car rim; some require tools, some require professional assistance and others -- if you're not careful -- can damage the tire, the rim or both. If you want to remove your tyre without paying for a professional, there are some tricks of the trade you should know about first.
Park your car on a flat surface. Engage your car's hand brake.
Loosen your vehicle's lug nuts with a tire iron. The car enthusiast website Dan O Land recommends loosening the lug nuts in a five-star pattern; this means loosening the first lug nut, then loosening the nut farthest away from the first, and so on. Do not remove the lug nuts completely.
Jack up your vehicle. You should raise the portion of the car where the wheel you're working on is located. Only raise the vehicle high enough to work on it; raising it too high can pose a safety hazard.
Remove the loosened lug nuts completely, once again using a five-star pattern.
Take the entire wheel off your vehicle's axle. Set it to the side on a flat surface.
Let the air out of the tyre. You can do this using an air pressure gauge. Though it is not necessary for you to complete this step, Adventure Rider suggests it, since it makes the subsequent steps easier.
Grease the area where the tyre meets the rim with a healthy helping of WD-40 or another brand of lubricant. Flash Offroad recommends putting additional grease on the area near the tyre bead. This is the edge of the tire, which sits in a slot on the interior of the wheel's rim.
Insert a flathead screwdriver or a crowbar into the seal between the tyre and the rim. Gently pry the tyre from the rim. Be careful not to break the beads; if this happens, the rim is basically useless for future use. You may need to use multiple screwdrivers or crowbars at multiple locations along the tyre/rim seal to get a lip.
Tug at the lip produced in step 8. You may need a second person to hold the wheel in place while you work on the tire. Work to get the entire tyre off the rim in this fashion.
Flip the tire over, and repeat steps 8 and 9. Once you've popped the seal on both sides, you'll be able to remove the tire from the rim completely.
You can also try walking on the tyre to loosen it from the rim, but any time you apply pressure to the area you make it more likely you'll break a crucial part. The word "best" is subjective. If you don't mind spending a little money, taking your vehicle or wheels to an tyre expert -- and having them do this for you -- could be considered the "easiest" way to remove a tyre from a car rim.