Upgrading To The Newest Version Of Zen-Cart and Best Mobile Friendly Template

I am running version 1.3.8a on the default template. Also running MMySQL version 5.0 and php version 5.2.17 and it has not been upgraded. We have only the ultimate seo url module, to my knowledge.

The questions that I have are, can you point me to an upgrading guide, that would tell me what are the main files that will need to have changes imported in order to upgrade to the very latest version? I would be going from 1.3.8a up to 1.5.7c. I am not sure how many changes there were in between.

Or is it easier to install an export/import plugin, and just import the database or products, and install a fresh new version? I would like to do this as quickly and easily as possible.

Can you please also tell me if there is a mobile friendly template that works well with this older version of ZC (1.3.8a)?

Also, what is the best mobile friendly template for the newest cart version?

As of right now, the site is not mobile friendly at all, and I am trying to remedy that as soon as possible.

Any help is greatly appreciated. Thanks!

To just upgrade without your modifications, use this guide:
https://docs.zen-cart.com/user/upgrading/db_only_upgrade/

This will give you the latest Zen Cart plus the responsive classic template.

Then make your language file changes and add in the latest Ultimate SEO URLs.

swguy:

To just upgrade without your modifications, use this guide:
https://docs.zen-cart.com/user/upgrading/db_only_upgrade/

This will give you the latest Zen Cart plus the responsive classic template.

Then make your language file changes and add in the latest Ultimate SEO URLs.
FWIW, for upgrading a version of USU that's that ancient, your best bet would be to totally remove the previous version's files and database settings and then start new. That older version of USU had a whole lot of tentacles that make upgrading that more difficult.

For a Zen Cart version that old (138a), I'd also suggest doing a "rebuild" instead of an "upgrade". There are many changes over the past 10+ years to the Zen Cart base that make an "upgrade" just too difficult. Unfortunately (perhaps @swguy can provide a pointer), I can't find the "rebuild" instructions in the updated Zen Cart documentation.

I'll also suggest using the Bootstrap-4 template (https://www.zen-cart.com/downloads.php?do=file&id=2191) instead of the built-in responsive classic. It's standards-based and, thus, is more conducive to styling- and layout-related changes.

The linked instructions were for a database-only update. As @lat9 notes, you really don't want to upgrade the old files you have - just start with new ones and add the changes you want in.

I feel the answers are not clear enough for a inexperienced user, "rebuild", "upgrade"...what do they mean?

Your site is two things: files and database.
The files look for and retrieve things from the database.
So an upgrade means
a) add or modify fields in the database: this gets done by the Zen Cart installer, automagically. Each ZC version may have these minor changes and the installer just adds them all.
b) add and modify the files for more functionality/better efficiency/better security. This has to be manually done and is a world of pain in proportion to the mods you have done/how much of overrides and observers have been used/your documentation.
This is also a source of white-screens-of-death when a new file looks for a new database field but does not find it as the database upgrade is missing something.

So, since there are masses of FILE changes from 138 to 157, the best course of action is to use a new ZC157 installation, import your database and upgrade the database, leaving you with a 100% up to date working site.
Then you can start adding your modifications.