To install it:

1. Unpack the xlam file from the zip file you downloaded
2. Close all Excel windows 
3. Confirm in Task manager that no remaining Excel.exe processes are running, if there are, kill them
4. Right-click the .xlam file and select Properties
5. Click the Unblock button or check-box near the bottom of the dialog.
6. Open Excel
7. Click File, Options
8. Click the Add-ins tab
9. Click the Go... button (close to the bottom)
10. Click the Browse button
11. Find the .xlam file and click Open

To use the file in one session, follow steps 1, 4, and 5 and open the .xlam and enable macros.