Changing your Tumblr username is actually quite easy -- the only catch is that it also changes your blog's URL. In many cases this isn't a problem -- you still keep your followers and continue following the same blogs you followed before. But any direct links to your old blog or blog posts will stop working unless you take extra steps to redirect your old URL to your new blog.
Changing the Username
To change your Tumblr handle, click the gear icon on your dashboard and then click the name of your main blog on the sidebar. Click the pencil icon next in the Username section, then type in a new username. Click "Save" and you're done.
Redirect Your Old URL
If you want to avoid losing viewers who may go to your old URL, act fast before someone claims your old username. Click your blog name on the dashboard and select "Create a New Blog." Enter your old username in the URL field and click "Create Blog." Once you reclaim your old username as the URL of a secondary blog, you post a message on the secondary blog that includes a link to your new URL. Alternatively, you can edit the secondary blog's HTML to automatically redirect visitors to the new URL.
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