First you need to resize this minikit to 128*128
You need to open the respective .big file (located in ur gui/assets/kits folder) using BigGUI, and extract the .fsh
Then you open the .fsh file using the fshED tool, select Tools Graphic Importer and select the minikit i just made... or use this one ( transparent and .png) (Old version of Minikit) If you wanna give it a try to the black background 1 do it
select update and then save and close.
Open the .big file and import the fsh back to your .big file using bigBUI.. save it and run ur game