Actually, I still like and use the old format. Simple and user friendly, IMHO.
Before you upload XML template file, ensure you have downloaded it. You can check my all cute template on this blog, then click on download link to get XML file.
Now I will show you the step how to upload XML file on new Blogger format.
Step 1: Login to your Blogger dashboard, and choose the blog you will edit. Click on Blog Title. For example, see on picture below, the orange color, Gadgetholic blog.
Step 2: Click on Left Menu, Template. Then, click on Backup/Restore button, on the right top window.
Step 3 : There's popup window, then click on Choose File button, and select XML file you want to upload. Now you get a new look design.