Hi Franziska,

There's not a lot of great tools/options to migrate from one version to another version in Odoo community. Your best bet is most likely OpenUpgrade (https://github.com/OCA/OpenUpgrade). Alternatively there's partners/services that offer an upgrade against a specific price. You can Google around for those, I'd rather not mention specific names or services.

If you don't use these kind of services your only other alternative is indeed exports/imports but that is a rather painful and error-prone process.

Regards,
Yenthe