File >> Import From Another Catalog
Suggest using the largest catalog as the master catalog and import the smaller one into it.
As you are using different machines you will first need to export the smaller catalog to an external drive and import from there.
Then physically move the image files and update the folder locations in the Library.
thanks for the explanation.
my catalog is located now on my hard drive (C). i want to move it to an external drive.
how do i do that ?
When you have combined everything on one PC simply copy the catalog (.lrcat file) and previews file to the ehd.
Then double-click on the catalog file to launch.