They'll need to be careful, as some Preferences are ' system-wide ' - for these,any changes will affect the other system users If their role has read/writer rights for Preferences (as above), they can set their own Preference settings. Then go to Manage Roles, find their role, then find General / Preferences and ensure it's ticked, with 'read and write' selected.
Find their user name and note their role. Hi can check a user's rights to change Preferences by logging-on as the Administrator, then going to Set-up / Users / Manage Roles.