I hope you don't mean load the latest version of firmware. That has a tendency to induce calls for help when it goes wrong.
You might first want to verify the H+ already has the latest firmware, then leave it alone if it does. If it is not up to date, it would be a good idea to review some of the related threads prior to attempting any firmware update.
Keep in mind the Forum has many tales from folks that bricked their machines trying to perform updates and calibrations they did not need.
I am not at home now. The best source would be the Yuneec Website for your area. Or just do a Google search for "Typhoon H Plus firmware update". The correct download page will be one of the search results.
Get conversant with the copter, leave Firmware alone, you need to make sure everything is OK, if you update then you have no idea if there is a problem, whether it was pre-existing, or the update has caused the problem. There's enough to get head around.