I think the files will be in a folder named "BeerSmith2" in your "Documents" folder.
1. Easy way:
Make a copy of the "Beersmith2" folder on the brewing computer. The copy should appear as "Beersmith2-copy".
Share the "Beersmith2" folder on your brewing computer.
Map a drive on your main computer to the shared "Beersmith2" folder on your brewing computer.
With BeerSmith running on your main computer, click on "File" then on "Change Documents Directory..."
Navigate to the drive you mapped to the BeerSmith2 folder on your brewing computer and select it as the new documents directory.
BeerSmith will pop up a window telling you that the files in the new location will be overwritten by those in your current directory. It's OK; that's why you made a copy.
BeerSmith will shut down.
On your brewing computer, delete the "Beersmith2" folder (or in an excess of caution rename it "Beersmith2-old).
On your brewing computer, rename the "Beersmith2-copy" to "Beersmith2". Share the folder exactly as you shared the old "Beersmith2" folder.
On your main computer ensure the previously mapped drive still brings up the Beersmith2 folder on your brewing computer. If it doesn't, remap the drive with the same drive letter. Sorry, I'm using Linux, so I can't confirm Windows will retain the link if you go through the process described above.
In order to use the BeerSmith data on the brewing computer, it will have to be turned on - sorry, that was probably obvious without me saying it. I'm guessing you're using a laptop for the brewing computer, so that may be configured to shut down after a period of non-use.
2. Hard way
Copy the "Beersmith2" folder on your brewing computer to your main computer. It can go wherever you care to put it.
Make a copy of the "Beersmith2" folder on the brewing computer. The copy should appear as "Beersmith2-copy".
With BeerSmith running on your main computer, click on "File" then on "Change Documents Directory..."
Navigate to the BeerSmith2 folder and select it as the new documents directory.
BeerSmith will pop up a window telling you that the files in the new location will be overwritten by those in your current directory. It's OK; that's why you made a copy.
BeerSmith will shut down.
On your brewing computer, delete the "Beersmith2" folder (or in an excess of caution rename it "Beersmith2-old).
On your brewing computer, rename the "Beersmith2-copy" to "Beersmith2".
This is the hard way because you'll have to copy files back and forth to keep the two machines synchronized. There are ways to automate synchronization, but this post is long enough already and I've forgotten how to do it on a Windows machine.