Tumblr is a very flexible platform. It allows you to create up to 10 additional blogs per day. However, you can always change the name of your main blog whenever you want. Changing a Tumblr name is the same as changing the URL.
Steps
Part 1 of 2: change your Tumblr name
Step 1. Be aware that the name change will also change your blog URL
Links to the old name will be invalid. To avoid this, consider creating secondary blogs instead of changing the name of the main blog.
Step 2. Choose the new name
Step 3. Add an additional blog to the new account to keep the old blog name
If you do not create an additional blog, the old name will be kept for 24 hours and then made available to other users afterwards.
Step 4. Don't worry, because you won't lose your subscribers
The name change does not result in the loss of subscribers, but it is best to let your subscribers know about the name change so that they are not confused.
Part 2 of 2: Change a Tumblr name
Step 1. Go to Tumblr.com
Sign into your account.
Step 2. Access your account settings from the dashboard
Step 3. Choose the blog whose name you want to change
Step 4. Navigate to the nickname section
Hover over this section to reveal the pencil icon. Select this icon.
In additional blogs, this section is referred to as the Tumblr URL section
Step 5. Enter the new name which will replace the old one
Select Save. Your Tumblr name would be updated.