Customise Theme without effecting Core Files / Modules / Upgrades HELP Please!

[applecart_girl]

Hi everyone

 

I'm able to change TPL and CSS files to customise the default 1.6 theme myself, however once I UPGRADE a module I lose some of my modifications.

 

I have looked through the PS guides and tutorials but can't find which files I should be editing so that they aren't effected by upgrades.

 

I think I may need to make over-ride file copies possibly? But not sure where to save them or how to set them up.

 

Can anyone tell us non-developers what to DO and NOT DO when making changes to a theme so that we can upgrade seamlessly as module upgrades are available.

 

Any hints, tips or links to articles on making changes to your Prestashop theme would be greatly appreciated, so we don't end up screwing up our stores in the long run.

Thanks so much