I have a Hyundai Accent 2014 and the user manual recommends to do a tire rotation every 7,500 miles. I'll be driving around 2,000 miles a year. Should I still do my tire rotations every 7,500 miles (which would be about 3 years and 9 months)? or should I do them more often since I drive very few miles a year?
What @HandyHowie says in the comments is spot on. You should most likely follow the manufacturer's recommendation on mileage and not worry about the time. Like he states, it's the wear which is important and time doesn't wear tires, it's distance.
NOTE: Dry rot will occur over time and not distance. Pay attention to your tires. If the car is kept outside (not garaged) this will happen sooner. This will happen whether the car is driven or not. To recognize dry rot, you'll see cracking in the surface of the tire, plus the tire will usually not be as black as a fresh tire, but look a little more grey.
The main purpose of rotating your tires is to ensure even wear. You can always rotate them sooner than manufacturer's recommendation, but if you do, still rotate at the same distance interval. (e.g. - If you rotate at 2000 miles, rotate them every 2000 miles.) If you don't, you'll cause the uneven wear you're trying to prevent in the first place. It's easier to just follow the manufacturer's recommendation, as this is a set interval and something you should be able to recognize and follow easily.
In your situation I would do a “rotation” once a year.
Rotation is limited by the type of tire, if they are assymetric or have a specified direction of rotation (winter tires are especially noted for this) then they can only move front to back etc.