mobile

Forgive me I am a noob. I recently rooted my AT&T S5 cause was waiting for the 5.0 update to come out. I decided to go back to stock and upgrade and removed the root all except the bootloader still appears with custom when starting phone and is only trace of root is all can seem to find but is keeping me from installing new 5.0 as it gets to 28% and restarts says unable to install instillation interrupted. How can I replace bootloader with stock one and where may I find one? Any and all help appreciated. I am running 4.4.4 android and is a SM-G900 AT&T S5 with kernel G900AUCU2AOA1.

Emt269