Download Blogger Template
Identify the XML file
A blogger template file should end with .xml extension. Your downloaded file may contain documentation and other links which is not compatible with blogger. So make sure you select template file with .xml extension.
Selecting your blog and Installing template.
Visit blogger.com or draft.blogger.com and login using Google account, you may asked to create a google account if you don't have one.
After logged in to blogger, select proper blog that you like to use our template.
How to Take Backup of your Existing Blogger Template
Click Download full template to take backup.
Upload Template (Refer the same pic shown above)
Select Template option from left sidebar (PIC ref NO:1)
Choose Backup/Restore Option on top right corner (PIC ref NO:2)
Take a backup of old template (PIC ref NO:4)
As shown in above click Choose File button and select the template file
Click Upload button
Now you completed the blogger template installation.