Database is too old and upgrade is required

Hi

I've installed a Sharepoint 2013 standard farm and it's been left for a while as other projects have taken precedence.  When logging back in I have several databases showing Database is too old and upgrade is required in the manage databases upgrade status in the UI.

In powershell I've run get-spdatabase and then used

PS C:\windows\system32> $olddb = get-spdatabase <ID>
PS C:\windows\system32> $olddb.type
PS C:\windows\system32> $olddb.needsupgrade

Against each database but it always returns false after each $olddb.needsupgrade.

How can I upgrade these databases?  A couple of the databases with this message are  Secure_Store_Service_DB_3c96ccb14d974dbaad3265db6f745792 and Search_Service_Application_DB_2b73539e670549719fa9f20f6438d8a8

Thanks,

Gareth.