Re-tinting a can of stain isn't recommended. But, you have a couple of choices that could change its color enough.
1) Use universal color tints. These are sold through many paint stores. Add small amounts to darken or change the stains color.
2) Take the can of stain to a paint store and ask if they will add some tint to change its color.
3) Buy another can that is considerably darker and mix the two cans to achieve a new color.
Buying tints or another can of stain isn't economical. You might as well buy the color you want. Plus, having a paint store re-tint the stain will be problematic. Most likely they won't do it or will charge for the service.
The cost of a quart of stain is small compared to the options or running around and wasting time to see if this is possible.