Check with your local Honda bike shop to see if the mufflers you want are available. Ask them what model is best for producing the particular noise level you desire. Consider using your local shop over finding parts online, as won't be able to ask for assistance in installing and maintenance. New bikes can come with this alteration already installed if you ask before purchasing your bike beforehand. You may also want to post to Goldwing forums online to get advice about which mufflers work best for the noise level you desire.
Check to see if the tail section and the seat need to be removed when altering or replacing the tailpipes. Then remove all bolts from the exhaust pipes and lay them aside. Remove the exhaust pipes, being very careful not to damage the port in which they fit -- fixing the port can prove to be quite costly, so be careful.
Take this opportunity to clean this usually inaccessible area of the bike well and place the new pipes into the exhaust port and reattach all bolts and brackets. Replace the seat and the tail section if necessary.
Start your bike and test the pipes. Use this opportunity to double check any brackets or bolts for looseness, as the engine should show you any weaknesses in your install. The new pipes should produce the desired level of decibels you have been looking for, but if not, ask your dealer for tips on how to enhance the sound level of your bike even further.
Recycle or sell your old pipes or give them away for free on Freecycle. More than likely, someone is wanting to obtain a quieter ride and will appreciate your offering them by online auction or for a low cost through a Goldwing forum.