This post shows how to update the theme of your blogspot blog, in the new, changed format of blogspot.
To start, download the template from wherever you want to.
If the template is in zip format, make sure you extract the file with format .xml and place it anywhere you want to, say Desktop.
Now, click in your blog's settings on Template.
Then click on right-top corner on Backup/Restore.
In the following screen, click Choose File, under Upload.
Customise the theme in your way.
That's it, You're done!