Keep in mind you can easy crush your instance if you not knowing what you are doing.
In this case I’d highly recomend let it go as it is. But if you want to try here are some links to follow:
running a mariadb cluster for more db peformence:
https://kaaproject.github.io/kaa/docs/v0.10.0/Administration-guide/System-installation/Cluster-setup/MariaDB-cluster-setup-guide/
switching to postgreSQL server instead:
https://markus-blog.de/index.php/2019/10/21/how-to-migrate-nextcloud-17-database-backend-from-mysql-to-postgresql/
its written for NC 17 and the schema of the DB has changed but the basic idea should be still working.
Information on HPB for Files: Setting up Files (High Performance Backend)
An NC update can be installed from the settingstab in your Webinterface.
I cant state often enough, that this not easy even for experts. So take a good backup to role back to if you crush the system ore let it run as it is.
“Never touch a running system, unless you absolutly have to” is a hard lesson to leasson to learn. Just keep that in mind.