In addition, for more help with Services (on top of the reference Poppy made) you can try the network's #Help channel and/or the network's website. If you don't know the network address the #Help channel should know, or search Google
. Remember, mIRC has nothing to do with network's services, they are unique to that network.
The mIRC options area (the 'Full Name' and 'Email Address' section I think you were referring to) is greyed out once you connect. You can disconnect and then go to options and change them, or simply type /fullname New Full Name
and /emailaddr [email]email@example.com
[/email] when you're connected, then next time you connect they would have changed. Once again, these have nothing to do with nickname registration on a network, they are shown with the /whois and CTCP Finger commands respectively.
Hope this helps :-)