My Flickr profile address is flickr.com/photos/theleanweb/ but I want to change it. Flickr only allows you to change your screen name, not your Flickr web addresses – so what can I do?
From the Flickr FAQ Page( https://secure.flickr.com/help/account/ )
Why can't I change the personalized URL I created for my account?
We're sorry, but it is not possible to change the personalized web address of an account once it has been set. Flickr has a firm policy on this in order to maintain data, metadata, and link integrity.
If you absolutely have to have a different personalized URL, you will need to create a brand new Flickr account and set the new URL there. You will then have to manually re-upload all of your photos to that new account. (Please note that there is no way to automatically transfer photos from one account to another.)