Users: you can have as many sub-User accounts for employees as needed, and this is highly recommended over sharing credentials for security, identity, and access control purposes. Simply go to Users (at the top) > New > User, and be sure to set the User Role, Manager has full access.
Password: you can define your own password under Users > Setup > Security, Go > “Allow user-defined passwords” (and any other options you’d like to utilize) > Save. Then click on your name in the upper right to select Change Password.
Primary User: you may change the Primary* User at any time via Users > Setup > Primary Contact, Go.