To rename your website name. You need to go to your WordPress dashboard area.
Hover over 'Appearance'.
Click 'Customise'.
And here will look slightly different depending on your website theme. If you cannot change it there.
I would click on 'Settings'.
Then 'General'.
At the top of here you will have you 'Site Title' and 'Tagline' options. This should change it to what you want.

Hi - if you mean the domain name of your site, which ends in .siterubix.com or .com, then it can't be changed.

If you are using a free website, you can delete it and start again. If you have purchased a .com name, you would have to buy another one.