Please backup your blogger template before you make any changes to it. This helps to revert back to the original template when something goes wrong while editing your template.
Steps to remove The Powered by Blogger text from your blog in the new Blogger interface:
1. Click on the Template link in the left navigation menu.
2. Click on the Edit HTML button
3.Select the Expand Widget Templates check-box
4. Remove the following highlighted code
5. Click on Save Template Button.
6. A warning is displayed.Click on Delete Widgets and click on Save Template Button.