For logging into manage.opensrs.net , you will want to send an email to support regarding getting the username and password to use.  You will also need to provide your accounts security verification information (last 4 digits of the card on record if you have a CC on record).

NOTE :  Changing the information in manage.opensrs.net only changes the whois information for your domain, does not change the billing.

If you are having someone else take over your hosting account, then you will need to change the billing information via account.lunarpages.com to their information.

If you are having someone else take over JUST the domain, then they will need their own hosting account and both of you contact support to have the domain registration billing moved to the new account.   If they have hosting elsewhere already, then they would need to contact their registrar/host and request a domain transfer to transfer the domain to them.