Hard to turn kitchen faucet: how to change the cartridge
That screw in the handle has to be removed with an allen wrench. Then remove the handle. The chrome dome piece then has to be unscrewed to expose the cartridge. There could be another brass nut to remove too before pulling out the cartridge. Remember to turn off the water before doing any of this. Hopefully there are shut off valves under the sink. If not, then you're looking at turning off the water to the house. Take it step by step and came back if you need more help.