If something prevents downloading files ending in .exe,
Download BASINS3.1update8.zip (11 Megabytes) then unzip it to get BASINS3.1update8.exe.
After downloading, exit BASINS then run BASINS3.1update8.exe to install the update. Installing requires system administrator privileges. This update includes all previous updates since the initial release of BASINS 3.1. Changes since update 7 include: