To enable AdXchanger on Tumblr, follow these steps:
1. Sign in to your Tumblr Dashboard.
2. Click Edit Appearance under your Tumblr in the Accounts menu.
3. Click the Edit Theme button to bring up the Tumblr theme editor.
4. Click the Edit HTML in the Theme section of the left menu.
5. Find the following line: </head>
6. Paste the following code into an empty line above the </head> tag.
7. Press the Update Preview button at the top right of the Theme Editor.
8. Click the blue Save button.
Need more help? Please don't hesitate to contact Tumblr's support team.