galaxy s5 unroot

Hi everyone, i'm having trouble downloading samsu stock firmware to restore my fon to factory. it takes hours to download and the files are corrupt. i am new to here so please be gentle. im trying to download G900FXXU1BOJ1 for my SM-G900F.......build num...LRX21T.G900FXXS1PPCF.......KERNEL........... .3.4.0-6531036.
any advice will be gratefully received. Thanks everyone.