I use Cubase Pro 9.5.2
Inside this came Halion Sonic SE3
Both need updating so, will 9.5.3 update Halion Sonic SE3 as well.
If not which should i update first ?

Run the Cubase Pro update. It will during the procedure notify you off which components are being updated, such as HS SE3. If it doesn’t list this then you’ll need to carry out the update separately afterwards.

OK that’s great.
Many Thanks planarchist