Mendix has a really convenient built in upgrade feature. If you open your 8.2 Studio, select Open App>Locally On Disk then select the mpr file of your “old” app, it will start to open it, and offer to automatically convert it to the latest version you’re opening it with. Bare in mind that big leaps between versions can sometimes cause errors/changes where things have been deprecated or amended between studio versions.
You also should be able to download any previous Versions here – https://appstore.home.mendix.com/link/modelers/ – to open your V7 apps with if you don’t want to convert.
Hope this helps!