First of all go to Google and in Google search “FREE DOWNLOAD BLOGGER TEMPLATE”. Then choose a nice theme and then download it.

Then go to blogger, in your site go to design. And then click on the “EDIT HTML” on the top of your Blog Dashboard. In that click on the  “BROWSE” then choose your template. After selecting your template click on the “UPLOAD”  button. Then publish your site by clicking “PUBLISH” button. Then if you visit your site, your new theme must be applied. And if you want to edit HTML, you can go back to same page and edit their.
                                                                       If You successfully changed your theme please share your Experience here.