How to install a theme - 2014
1) Choose a theme you wish to use on your tumblr.
2) Purchase your theme and create an account.
3) Your latest theme will be at the top of your downloads list. Now click the green download button.
4) You will now be able to see your theme code.
5) Ok, now open a new tab and log into your tumblr account and click the customize button.
6) Click the "edit html" button and you will see a page like this.
7) Select all the code, delete everything and press "Update preview"
8) Now type in the word "reset" and press "Update preview", this will remove any defaults.
9) Now go back to the Theme Code tab and copy the code.
10) Now go to the Tumblr customize page and paste the code in.
Don't forget to make sure the word "reset" is removed.
11) Press save and your theme will be installed.
You can play around using different options to give your theme a more unique feel.