vQmod

However GrandCMS have its own modification system OCMOD, what is exactly the same as in OpenCart (from 2.0.1), you can use the good old vQmod too.

vQmod have more feature than OCMOD.

Install vQmod is easy. You can download the 2.5.1. version from here.

1. Just copy the vqmod folder from the zip file to your web root directory.
2. Goto http://www.yoursite.com/vqmod/install

You should get a success message. If not, check file permissions and try again.

Here is  a detailed description: https://github.com/vqmod/vqmod/wiki/Installing-vQmod-on-OpenCart