Here are some images to help you better understand the parts of a reed and how and where to "work on them". I would recommend on the cheap end, 600 grit sandpaper as a basis for your work. If you have money, get some reed rush and then a reed clipper. More money? ...get the Vandoren glass reed tools. As a general rule, avoid the heart of the reed (the red).
The reeds above show the "general areas" to adjust and balance for the ranges you feel sluggish or unresponsive. As a general rule, most people start out their reed adjustment adventures balancings in the upper range area in the right-most reed (lowest reed on mobile device). When you see people doing the "side to side" thing where they turn the mouthpiece and play on one side at a time, that is the area (high) they end up adjusting in.