Working on the clutch of the Nissan Altima is something you can do yourself. You can fill the level of the fluid in the reservoir, bleed the system and even replace clutch components to improve its performance.
Check the level of the fluid in the Nissan Altima as the first step in adjusting your clutch. It may just be a matter of adding fluid to the indicated line, then pumping the clutch pedal to restore the hydraulic pressure in the line.
Bleed the clutch system by opening the bleeder valve on the slave cylinder. Insert a tube, and put the other end of the tube of a clear container with clutch fluid. Have someone pump the clutch pedal until you see no air bubbles in the container. Check the level of the fluid in the reservoir again, and if it's low, add more fluid.
Examine the slave cylinder in your Nissan Altima. If you pull back the rubber "boot" and find that it's leaking, then you should replace it, as no amount of adjustments for the clutch would help until it's replaced.
Replace the master and slave cylinders if the clutch will not stay adjusted as you would like. Parts become worn, over time, and they meet the end of their usefulness and effectiveness. You will find that the clutch of your Nissan Altima will work well after this is done.
