How to Go Back to the Regular Tumblr Themesby Alan Sembera
Playing around with custom Tumblr themes can be a lot of fun, but eventually you may want to return to a classic theme from the Tumblr website. The standard themes, while lacking some of the fancy graphics of designer themes, often support more features that are standard and can be easier to use. You can install the regular themes from your blog's customization page. You can also reinstall the same theme to undo changes you made to its HTML code.
Click "Customize" on your Tumblr dashboard.
Scroll to the bottom of the Customize pane and click "Advanced Options." Delete any code in the "Add Custom CSS" section to remove any theme customizations you added. Click the back arrow at the top of the pane to exit the advanced settings.
Click "Browse Themes" to search for a new theme or restore your current theme to its original settings. Tumblr displays a list of free and premium themes, along with a thumbnail of each theme layout.
Select "All Themes" and then "Free Themes" to see only the basic, free themes. If you already have a theme in mind, click the search icon and enter the theme's name. To use the original blue Tumblr theme, enter "Redux." To use the current default theme as of January 2014, enter "Optica." Other free basic themes include "Default," "Optimus," "Papercut" and "Simple Things."
Click a theme to select it and see how it looks in the preview pane.
Click "Use" and then "Save" after you find the right theme. If you selected a premium theme, click "Purchase" and enter your credit card or PayPal information. If you reinstall a premium theme you purchased previously, you don't have to pay again. Click "Exit" to return to your dashboard.