You've got the general idea, anyway. Some of the files in those groups should be animations (all the ones that end in
da). Chances are you want to leave those alone...
If you double click on a file in LGP Tools, it should give you the option of trying to view it. Try to view each non da file in the two groups as .P (3D data) and .TEX (textures). Take notes, especially because if LGP Tools finds a file it doesn't know what to do with, it'll probably page fault.
The reason for doing that is because the file names might not match. This is just something I'm pulling out of thin air (AKA as a Dilbert "assumption") but suppose sidd is part of high res Cloud's head. Now, if you just rename sidd to rtdd, it might turn out that rtdd was part low-res Cloud's arm...
You've got to figure out what each part is first.
So you want a list of each part for both models, and their names. Something like this:
Part: High Res Low Res
Head sidd rtsr
Head Texture side rtss
Left Shoulder sicf rtmb
...etc. I made up those filenames. Just making a point.
Then you can start swapping. I recommend loading up the game and trying after every change you make, just to make sure.
how do I import by the way?
Click on the file you want to replace. Then hit the big "Replace" button in the upper right, which will bring up a dialogue. Browse to the file you want to replace it with. Voila! Isn't Ficedula cool?
After I do this I want to make a patch so I can give it to friends and they can use the high-res model. How do I do this?
Go to Tools > Patches > Create Patch. I recommend using the Pack Archive option in LGP Tools before this. To create the patch, you'll need an unaltered copy of the .lgp (from one of your game discs) for LGP Tools to compare it with.
I've sometimes had trouble getting it to create the patches in the past, so check the size of the patch (should be about as big as the files you import), and test it, before distributing. If you have problems, try changing the directory where LGP Tools saves the patch.