Go to Account Settings Edit Appearance Edit Theme.
Click on the Edit HTML link underneath Custom Theme.
Paste POWr Script
Paste this exact POWr script into your HTML file, in between the Head tags. Then click on Update, and save.
Create New Text Post
Go back to the Tumblr dashboard and add a new Text post.
Paste the Shortcode
Paste the shortcode into the post. Then save. If you expand the post, you will see your new POWr Image Gallery. Click on the Settings Icon to launch the POWr Editor.
Begin customizing the following Image Gallery Plugin right in your Tumblr website:
Go to your live Tumblr website and select the Settings Icon in the upper right corner of your Image Gallery Plugin.