Upgrade from 1.3.0.2 to latest with database mods

Hi all, i have looked at this before and decided against it, but i really do need to get round to this u/g.
My main concern is we have modified the db (additional fields in existing db's and new tables etc) and written our own management and packing system, ie auto upload of shipping data, barcode scanning etc.

I did previsouly try to manually adjust the db so that both carts (ie v1.3.0.2 and 1.3.9 could work side by side for a period, but i was told this was a bad idea and i should perform the upgrade as documented. My concern is this will undo the 3 yrs or so of dev work that has gone into our managemnt backend while zen quitely got on with the important stuff.
Just to be clear zen has not been modified but the db's have.

Any advise?

Just to be clear zen has not been modified but the db's have.
I think you will discover that your code has also been modified to interact with your DB changes/additions

1.3.0.2 will be a larger task to bring upto 1.3.9g

Follow the tutorials, and create a "test upgrade" install where you can insure all is right before using the upgrade
https://www.zen-cart.com/tutorials/index.php?article=98
https://www.zen-cart.com/tutorials/index.php?article=108

Kobra
Thanks for the reply.
There were no mods made to zen (i know i did the .net application) all it does is read zen info and writes to additional fileds etc.
I purposly made no zen mods in the hope that it would be an easier upgrade. I will create a test site as you recommend.

Also as a question the sql upgrade scripts etc, will they remove the additional info from the db? or just chnage the ones zen uses

"the sql upgrade scripts" should NOT be run "by hand". You should run zc_install as per the upgrade instructions. This will retain the database content as-is, and upgrade just the components requiring upgrading to be compatible with the new version you're upgrading to.

great news. I will copy the db etc and try an update.

Ill let you know how it goes

many thanks

James