A faucet that has weak water pressure for both hot and cold water may just need the aerator cleaned. Another symptom of a dirty aerator is an irregular spray pattern or a stray stream of water going off at an odd direction. Cleaning or replacing the aerator is very easy and you might be able to do it without any tools.
First of all, close the drain so you don't lose any parts. You don't need to turn off the water supply for this repair. The aerator is the assembly and screen water passes through as it leaves the spout. This part at the tip of the spout unscrews in a clockwise direction (righty tighty, lefty loosey). Dry both the spout and your hands before trying to remove it with your fingers. If it is too tight, then you are going to need to use adjustable pliers. Before using the pliers on the faucet, wrap several loops of masking tape or a rubber band around the aerator to reduce the risk of marring the finish.
Once you remove the aerator you will notice one or more parts contained within. Note the order and orientation of the parts as you remove them. As you take them out you will probably find grit and rust. Rinse the pieces with water and brush off the debris. For difficult to remove deposits, soak the parts in white vinegar for a few minutes and scrub with a toothbrush. If any parts are cracked or broken, replace them. If the washer has hardened, it should replaced.
With the debris cleaned out, reassemble the aerator and screw it back onto the faucet. Hand tightening should be adequate. If water leaks around the threads, give it a fraction of a turn with the pliers and then remove the masking tape.