Need help getting som controll who gets access to server - repost

Hi , I need this to be done : :) 1: Create another ftp account that has direct access the the ssh client keys, so i can remove public key and add new public keys. 2: Show me how to change password for the ftp users that i have, 2 users...the one your will make and the one i already have 3: Show me how to give access to a new ssh user(true public ssh key) and how to remove access. I need to know these things so i can restrict access to server whenever i need to. Hope you can help me with this :) its not urgent, so whenever you get time.