It is at the same place as the unit software updates on the Humminbird website--
Software Update - Humminbird PC v. 4.6.1 - Humminbird (johnsonoutdoors.com)
Wayne Purdum
Charlottesville, Va.
Helix 12 CHIRP MEGA+ SI G3N/G4N, Helix 15 CHIRP MEGA SI+ GPS G4N
SOLIX 12 SI/G3, Helix 8 CHIRP MEGA SI+ G4N, Ultrex 80/LINK, MEGA360,
MEGA LIVE, LIVE TL
Wayne Purdum
Charlottesville, Va.
Helix 12 CHIRP MEGA+ SI G3N/G4N, Helix 15 CHIRP MEGA SI+ GPS G4N
SOLIX 12 SI/G3, Helix 8 CHIRP MEGA SI+ G4N, Ultrex 80/LINK, MEGA360,
MEGA LIVE, LIVE TL