Is there any guide on how to migrate the Database of the SCCM Secondary Site Server to a new SQL Server?

Hello All, I have a task on my client for migrating the database of the secondary site into a new full SQL server. The existing secondary site uses a SQL Express and we have some issues specially on the database size limitation for WSUS DB and the Secondary Site DB. I have google a lot but i dont see any particular guide on how to migrate to a different server. Please share any documents or guides on how to do this. Thanks Everyone!