To change the blog template, please find a template you like in btemplates.com then save it to your computer.Then go to your blogger account, select a template and click the back up / restore, as pictured below.
After that the menu will appear as shown below.
After that, press the search button and then locate the template file that has been saved earlier. and enter the formatted xml file and press upload to replace your template.
Press the view blog if you want to see the template that you just plug into your blog.