I have been asked by a friend for instructions on the best way to handle her catalog when moving between her homes in the US and UK. She has been updating her catalogs from one catalog to another and feels it’s a pain in the neck. She's not the only one. If you use 2 different computers & share a catalog the easiest method is to keep your catalog as well as your photos on a small external drive, which you can carry with you between computers.:
Firstly move your catalogue from your computer hard drive using Finder/Explorer. To do this, go to Lightroom (mac)/Edit (PC) > catalogue settings > General > Location - show. It will take you to your folder in explorer/finder then you can move the folder to your portable drive.
Once you have moved your catalogue folder go to Lightroom (mac)/Edit (PC) > General > Prompt me when starting Lightroom.
Then when you next open Lightroom you will be prompted to choose a catalog. Select Choose a different catalog and select your catalog, it will then appear in your list to select every time you open Lightroom