This is easy to use and simple step to change your template just follow this instruction: But you have to know that when you change your template, most templates that you will choose from my blog Zenplate or other website provides you templates do not have navbar ( you will can not logging to blogger directly).
First, choose 1 template from my site(Zenplate) that you like then click "Submit", yes you will see the whole code.Leave it a moment...
Then, go to blogger.com---->loggin---->Layout---->Edit HTML
Look at your old and boring template code the last time,copy the new code that you have chosen before and paste it instead of whole old code in "Edit Template" frame.See the picture:
Then click Save template and join with your new template Very easy right ? Good luck