IRC Freenode Changing Your Account Name

Set up a nickname

/nick

Change your group

/msg nickserv group

Then set your accout name by:

/msg NickServ SET ACCOUNTNAME

For some info, you can do:

/msg nickserv help set accountname

/msg nickserv help group

Note: Freenode allows you to mask your domain name so it'll end up to unaffiliated/ instead of your public IP address or your domain name which is isn't safe.

Hope this helps!