Hi Adam,
may I suggest something: If you have saved or scheduled reports it makes sense to seek a migration. But if you don't have those (like most customers), why just not do a new install? Its easier, quicker and cleaner.
SSRS installs the Report DB and the Reortt Temp DB, those actually do not contain any data besides what you jave saved (favourite reports, scheduled reports, custom reports, etc...). The actual data is in the Data Warehouse.
So, if you don't have any of the above mentioned report types, just uninstall the old version, install the version you need and all the standard reports will be populated again.
I hope I could help you out!
(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)
Regards
Stoyan Chalakov