How to change a machine name?

[joe at actionline.com]

What is the procedure to change the machine/system name?

For example, one of my computer's names that appears at the prompt is:
joe at joe-T60:~$
I'd like to simplify it to just t60:

Likewise, I'd like to change my other computers machine names to simpler
names.

Also, is it possible to change the ip addresses of one's computers and
other devices; and if so, how can that be done?