G'day mate, welcome to GPS Power!
For starters, I would not delete any maps from your nüvi 2597. It does not simplify any of the steps you still need to take! However, if you can not resist the urge to do so, then at least make a backup (copy) of those files before deleting them. You'll find the factory loaded map in the hidden .System folder, most likely by the name gmapprom.img. Make sure to backup the associated .gma and .unl file as well, as they go hand-in-hand with the .img map file.
Depending on the HWID (hardware ID) of your nüvi, it may need patched FW (firmware) before it can accept unlocked maps. Have a look here: [Only registered and activated users can see links. ]
If and when your nüvi is capable of accepting unlocked maps, start reading here: [Only registered and activated users can see links. ]
The latest map of North America (including Hawaii), can be found here: [Only registered and activated users can see links. ]
To keep things simple, I recommend you use the unlocked map on a microSD, placed in a root folder named Garmin and the file name gmapsupp.img.
Alternatively, you may place the unlocked map on a microSD in a root folder named Map and the file name anyname.img (it can really be any name, as long as the file extension is .img).
Considering the amount of "homework" to do, you may realise you initiated this process a little late, at the eve of your trip. Nonetheless, the above information may still be of use for future trips as well as for other members coming across this thread.