As long as the Humminbird unit supports the GPX format, you can just export them from the Lowrance unit in that file format.
One caution, check the waypoint names. If any are longer than the Humminbird format has room for, have any with spaces or symbols in the names, they will be corrupt for use and may cause unit operation issues.
I received a .usr file with over 900 waypoints to review and had to edit about 1/2 of them. Still have some that cause a pop-up warning when opening that file in HBPC. Since I am not using any of them, I am not concerned about it.