Ok, as the resident vinyl graphics expert (no seriously, it's a big part of my job) it's a pretty simple scenario.
On a new decal, as most Carmax vehicles are, temperature isn't a big deal. The vinyl is still soft and pliable and not prone to cracking. A little heat will soften the adhesive a bit and make it easier to remove, but may make it a little more likely to leave adhesive. Cheaper films are more prone to delamination, which is when the adhesive separates from the vinyl face.
Just use your fingernail to start lifting an edge until you can grip it with your finger. Then pull slowly and at a 180 degree angle from the surface (kinda of fold it over and pull away). Going too fast will often result in the vinyl snapping and having to start over. In my experience fingernails work substantially better than plastic scrapers. The vinyl remover balls you can buy at a hardware store are WAY overkill for an application like this, and are really designed for removing graphics from an entire commercial vehicle. They tend to leave lots of adhesive behind also, which is harder to deal with then just peeling the vinyl correctly in the first place.
For adhesive removal, I want to clear up a few mistakes in this thread. The absolute BEST product is 3M Automotive Adhesive Remover. They also make a citrus cleaner that is almost identical. Goo Gone and Goof Off are perfectly fine for removing acrylic based adhesives on paint. The key is to not use paper towels, and to minimize scrubbing. The 'damage to paint' people often report from using citrus cleaners is actually a product of the paper towel fibers scratching the surface from excessive rubbing, not the adhesive remover. Your best bet is a clean cotton towel.
Also people often misuse adhesive removers. It isn't a spray on, wipe off endeavor. You could saturate the area with remover, and then allow it to sit for a full minute. This will weaken the adhesive and release it from the surface. Use a squeegee or a credit card to scrape up the adhesive (it will come up in clumps after sitting) DO NOT smear the adhesive around with your towel. Once you have a majority of the adhesive off, go back with your remover, saturate the area, wait a minute, then wipe off the remainder with your cotton rag.
Apply wax to the area immediately, and you are back in business.
I know this was a very long drawn out explanation, but it should address any concerns about removing vinyl graphics and clear up any misinformation that is commonly spread around. The whole process is very easy if you are using the right tools, and using them correctly.