PrestaShop introduced automatic upgrade in version 1.4.4 and 18.104.22.168, which was then turned into a free module for earlier versions (starting with PS 1.3) and later versions (including 1.5.x).
Note that this module is still experimental. Use at your own risk.
If you'd rather be safe, take the longer but more detailed manual instructions instead.
Downloading and installing the Auto-Upgrade module
Simply follow the normal path to installing a module on PrestaShop:
You're done! Now start configuring!
The Configuration Screen
If you have the latest version of PrestaShop already, the tool will simply display "You currently don't need to use this feature."
- Don't save images: the upgrade process normally doesn't touch your images folder. If you have made a proper back of all your files, you might wish to let the process take care of that folder too, in order to have a clean install again and re-upload your files. Nevertheless, it not recommended doing this.
- Keep theme "prestashop": the upgrade process overwrites the default theme with its latest incarnation. If you have made changes to the theme directly, you can protect these changes by choosing "Yes". As a reminder, it is NOT recommended to edit the default theme! You should make a copy of the theme, and make changes to that copy.
- Keep translations: same as for the default theme, if you have made changes to the PrestaShop translation files, you can protect these changes by choosing "Yes".
The Upgrade process
The update button itself is at the center of the page.
Is everything working fine? Congratulations, you know have successfully upgraded your PrestaShop install!
Sadly, not all upgrades are successful – which is the very reason why you should always backup all your files and data, and why PrestaShop performs an additional backup of said files and data itself (which you should not always count on, obviously. Make your own backup first).