When you migrate your old classic Blogger account to the New Blogger account, your blogs will still be using the old classic template. To take advantages of the new features of a New Blogger template, you will have to upgrade your old classic template to the New Blogger template.
Sign into Dashboard. You will see a list of blogs. Blogs with old classic template will have a link "Template" (circled in red in screenshot below) while blogs with New Blogger template will have a link "Layout (circled in red also):
To upgrade to a New Blogger template, click on "TEMPLATE" and then below the TEMPLATE tab, click on CUSTOMIZE DESIGN, then click "Upgrade your template". You will then be presented with a choice of templates. Select one and save.
Don't worry too much about your choice of template. You can easily change later. And if Blogger standard templates are not good enough for you, there are now plenty of New Blogger templates to chose from. Here are some of them (click BACK button to get back to this page:
New Blogger 3 column templates modified by Stavanger
Dots 3 column template with Header modified by Stavanger
New Blogger 3 column templates modified by Ramani
New Blogger 3 column templates by Isnaini
3 column New Blogger templates by Thur
Ramani's New Blogger Neo template
New Blogger templates by Final Sense.
(Note: Blogger will backup your classic template when you migrate to New Blogger template so that you can revert to your former template if you want, but it is advisable to also copy the template from the template editor, paste it into Notepad and save it. Not only will it serve as an extra backup, some of the customization you may copy-paste into the New Blogger Page Element or direct into the template depending on the case, thus making your task of getting your previous customization easier.
