Changing your Tumblr URL is very easy. First visit the Tumblr webpage. Next click on the little gears symbol on the top of the page. Next click on the tab near the left side of the page underneath the "Apps" tab. Next delete the old URL in the URL box and type in the new URL you want to use (as long as it's not taken). Then click "save" on the right hand side or bottom of the page. Once you have done this you have a new Tumblr URL.