Hi Patrice, I've only ever set up one PowerStore site which it was a long time ago and the site doesn't exist any more, however from memory it uses the same setup and files as building a cart from scratch using eCart. I have one eCart site which I've recently upgraded to PHP8.2 with very few issues. If it's already on PHP7 then you shouldn't need to do very much at all, but if you're still on PHP5 then you will of course need to upgrade all the server behaviors to mySQLi before going any further.
My advice would be to clone the site onto a testing domain on your server if possible, make sure the testing domain is running the new PHP version, then go through the cloned site and check for anything that doesn't work, adding error reporting to the offending pages. Also use View Source in the browser as sometimes an error won't display, but you can see where the page stops loading in View Source. One issue I had was on the product detail page which was just showing a white screen and no errors - but when I went into View Source I could see it was the dynamically-generated meta description tag that wasn't working. Recoded that bit and the site was fine!