Error on Upgrading from 2.1.x to 3.0.1.2

Hi,
I am getting error while upgrading from 2.1.0 to 3.0.1.2. The error message on accessing http://<yoursite>.com/install is

Notice: Error: Could not load template /home/u794139114/public_html/onlineshop/install/view/template/common/header! in /home/u794139114/public_html/onlineshop/system/storage/modification/system/engine/loader.php on line 97

How can I fix this or should I restore the opencart back to its previous state. Any early reply could help.

Yoru need install default theme from admin 》extensions

I tried with the default theme and it is giving me the same error..

I am still getting blank page on htp://yourstore/install . Can anyone just help..