How to modernise this raised concrete drain in the middle of patio?
Yes that appears to simply be set on top of a spacer which is then set on top of the buried box.  You should be able to lift it off, with some effort, and also keep in mind that some adhesive or mortar might have been used to secure it.

It looks like you should be able to remove the spacer under the lid and drop the thing down a few inches to make it flush with your surface.

A local concrete product supplier may be able to provide a nicer lid but some adapting may need to be done it order to get it to fit right.