What's a GEDCOM file
A GEDCOM file contains genealogical data in a standardized format. Most Genealogical programs can extract the data needed from a GEDCOM file .... but beware! It will probably add the contents of the GEDCOM file to your existing file.
To ensure that your hard-earned data is safe, follow the following steps:
1 - Backup your current data.
2 - Open a new file (probably File-New).
3 - Download the GEDCOM file and save it on your harddrive.
4 - Import the GEDCOM file into your new file.
5 - Compare the new data with the data in your existing database.
6 - Select the appropriate individuals in the new data and create a new GEDCOM file (probably some form of a File-Export command).
7 - Import the smaller GEDCOM file into your database.
8 - When you're satisfied that you have ONLY the data you want, backup your database.
9 - Repeat steps 6 - 8 as often as necessary.