Depends on your registrar but you should be able to do this from your domain registrar's control panel. Typically you change the contact name in your account and it cascades to all domains in that account.
yes, you just need to login to your customer control panel. You can change the whois contact information there.
Almost registrar acept you change domain contact info. Login to your domain control panel and find it
Correct, it depends on who it's registered with - and sometimes you have to call in and talk with them personally, aside from changing it through a control panel.