The Space Construction Tech advises you get access to a new version of the Small Spaceport.
Basic Orbital Assembly

Space Construction Tech

I went in to manually update the first space port I built.

However it was still limited to the max size of 750 with no way, that I could see, to simply update the station to the larger size.

When I went to add new on the design window I was able to see another small space station there with all the correct stats.

Now I was initially thinking this tech should just be a straight upgrade to the Original Small Space port simply updating the original Stats but from this it looks like it is just adding a new template from which we have to start the design from scratch again.
If anyone else could advise if they have the same issue.