I think they are just in order. So if you want to remove a P51d skin "506FG/458 FS" you count down the list. If it is the 23rd in the list then removing the "p51d_23.res" file would remove that skin.
Another way to do it would be to go here.....
https://bbs.hitechcreations.com/skins/Select the plane type in the drop down box.
The next page will have all the skins for that plane/vehicle. Click on the picture of the skin you want to remove/save.
When on that skins page, hover your mouse over the download link for that skin. In the lower left corner of your screen a windows box pops open showing you the name of the link address. The last part of the address is the "xxxx_xxx.res" file that is for that skin.
Remove the skin using the file manager.
REMEMBER...... uncheck the "download skins automatically" check box in the game or it will just add all the skins you remove again.
