In the PCB editor, File menu about half way down there is a 'Renew Layout from Schematic' Selection. I think that is what you are looking for to reflect the changes made in the schematics. When you select 'by RefDes' or 'by Components' it will ask you to select the schematic, just pick the proper schematic and it will update. You might want to play with that a bit and see what it actually does. Be careful with this, as I recall I hosed something up when I was first fiddling with this.
I also use the 'Convert to PCB' feature to get the PCB started. Diptrace is good at auto-routing, but not so good at component auto-placement. I place everything and just let Diptrace do the routing.
GRJ, thanks for the screw terminal file, I found a couple by searching the internet, but they all gave me 'file not compatible' or similar errors when trying to get them into DT. So that was a fail...
