Blogger provides XML templates and you will find tonnes of third 
party templates on the internet. You might also want to tweak the 
templates to change the way how your blog looks. Before you make any 
changes to your template, it might always be a good idea to take a 
backup of your template. This will allow you to restore it back in case 
the template edit did not go well. Backing up restoring templates on 
blogger is very simple using the new Blogger interface. In this 
tutorial, we will guide you through the process.
How to take a backup of your Blogger Template
Like we said earlier, it’s always a good idea to backup your template
 before you make any changes to your Blog’s template. Below are the 
simple steps which can help you in taking a backup of your blogger 
template.
1. Login to your blogger account, and go to the Template section in the blogger dashboard(for that blog)

2. Now click on the “Backup/Restore” button on the right top of the page.

3. You will see a popup with an option to download the current template. Click on that button

4. You will get a backup XML file with the name 
template-somenumber
.xml . Keep this backup file safe so that you can restore it when required.
How to restore the Blogger template from a previous backup
In case you have made some changes to the template and that has 
messed up the way your blog looks, you can restore the old template from
 the backup file which you might have created. Below are the steps to 
restore the template from a previous backup.
1. Login to your blogger account, and go to the Template section in the blogger dashboard(for that blog)

2. Now click on the “Backup/Restore” button on the right top of the page.

3. You will see a popup with an option to upload a template from your hard drive
Now select the backup XML file which you had downloaded earlier while
 taking the backup.Once done the Upload button will be activated. Click 
that button to upload the backed up template.

Once the upload is complete, your old template should be back in action