I need to lower my 2005 Goldwing ... have no idea how to do this.

In my case I am very tall and the prior owner was short and cut the seat foam. I went to a motorcycle seat builder in Bainbridge New York and worked with him to add and remove foam as needed in various parts of the seat till I found a nice height and comfort. Total cost $75.00 I also had seen a couple of seat builders at Americade in Lake George NY that offered similar seat work. You might be able to find a seat builder in your area at a trade show or try online. My riding buddy has an after market air ride seat he purchased for $750.00 for his Goldwing that lowers about 4 inches with the press of a button then self inflates as needed. There are many companies out there that offer after market seats and seat rebuilding that can help.

You may be able to modify your seat by removing some of the padding, and recovering it. Aftermarket seats may also be available.

Very slight adjustments in height can often be achieved by moving the fork tubes in the triple clamp. Note that this will affect the handling characteristics of the bike. This modification is not recommended for safety reasons.

Another alternative is to wear boots with an extra thick sole.

In any of these cases, the difference in height is going to be relatively small -- a couple inches at most. It is important that your bike allows you to feel comfortable, confident, and that you can control it fully at all times. Although it's not a very satisfying solution, the best solution might be to find a bike with a lower standover height.