Just a heads up: changing your URL will break any existing links to your blog, including those in already-published Tumblr posts and reblogs. Your followers won’t be affected, though, and they’ll still see all your stuff come through their dashboard.
In the app:
- Tap the account icon (the little human).
- Tap the gear wheel icon.
- Tap "Change username."
- Enter your new username.
- Hit "Save."
On the web:
- Click "Settings" under the account menu at the top of the dashboard.
- Click the blog you’d like to update on the right side of the page.
- Click the pencil icon in the username section (or Tumblr URL section on secondary blogs). Adjust your URL as you see fit.
- Hit “Save.”
If you have trouble saving the username you want, it may be because the URL is already taken.
And by the way: after you save it, we still hold your old URL for 24 hours, just in case you change your mind, or you want to use it on one of your secondary blogs. After that, though, your URL is released into the wild. Wish it well.