If you're on steam (like me), install directory is accessed through 'My Computer -> (C:) -> 'Program Files' ('x86Program Files' for some) -> Steam -> steamapps -> common -> arma 2 operation arrowhead -> Expansion -> Battleye'. Paste the 2 DLL downloaded files here and overwrite the old ones. If you're not using ARMA II on steam, find the install directory by the same process but exchange the steam-apps-common etc. with wherever it actually is. To be honest, I don't know if there's a 32 vs 64 bit difference with these files.