depends on your data. if you have just a “couple” of file store in some folder it should be easy to “backup and restore” via a client. sync everything to your pc, install nc13, setup the desktop client for this and move the files to that folder to upload them to nc13.
if you have a lot of files, a lot of users, a lot shares and such stuff you need a proper consistent backup.
what kind of backup do you have? you need the data folder and the database. preferably taken at the same time.
but the bad news: to restore a owncloud backup to nextcloud and migrate is no fun. i did it. so i know.
if you want to test the migration my advice would be: get a aws/azure/ovh/digitalocean/your-fav-cloud-provider account and try either to downgrade/restore there your owncloud installation to an upgradeable version or install nc13 and just migrate your data. Make a backup of the result and restore it to the server where you want to run your nc.
(you may find https://github.com/ReinerNippes/nextcloud13 helpful to install nc13 in a cloud server.)
From time to time they update the migration schemes. So if you stay with 10.0.8 a bit longer, you might be able to migrate directly. Lately it gets a bit more messy because Nextcloud pushes out new versions and does not backport new features to old versions while ownCloud tries to keep only one version and pushes changes in minor updates. So you have to look carefully between which versions an upgrade is possible.
If you want to move quickly and don’t have a lot of data, a backup of the data and playing them back to a new Nextcloud setup could be the easier and more secure solution.