Scroll down to the 540 Section and download the one you chose.
It must be 2d profile at 0.83v and 3d profile at 0.85v. preferably the A09 version.
It is a delicate opperation, only attempt if you are out of warranty and after reading the instructions properly ( dont forget to check the checksum), if you folow the intruction you shoudnt have any problems.
It is only for the XPS 15 L502X and nothing else, dont try to flash the bios on a wrong hardware.
I am playing now for 2 days on ac power without any crashes, also noticed a big drop in gpu temperature and more stable performances.