Upgrading from 1.5.1.2 to 1.5.3.1

Hi guys,

I'm planning to upgrade my current version of OC to the latest one and to change the theme. I saw the "step-by-step" upgrade tutorial but my question is - is there any way of upgrading to the new version and to do a clean install of OC with the old DB? The problem is that I made some modifications (added some features) and I don't believe that the new theme will work correctly...

Yes, you can delete all of the OC files off of your server except the config.php and admin/config.php files. Download those two files to your computer. Then upload your new version of OpenCart. Once uploaded, replace the default config files with the ones you downloaded from your old install. After that you're good to go.

Is this the "better" choice to do upgrading. Then why there is upgrade tutorial??? Aren't the tables going to be messed up with the new version and the new template?
I have also VQMod extension. What about this one?

You could export your old db, create a new db, do a clean install and link it to the new db, and then import your old db to the new one.

Kinda confused on what you want though. If you want to upgrade to the new version, then just follow the upgrade tutorial. If you are worried about your theme not working, then just delete the theme or change to another one.