Replacing Bootloader 6 with 7pre4?

[kefs67]

Hello,first time poster, so here goes,
yesterday i decided to have one last attempt at resurecting my H140 after 18 months of non booting up, just the red read light constantly on. To my absolute surprise, with power applied, it actually started up and although it shows 0000 files, when connected to PC i could view all 40gb on it, so slowly i started to delete all files. 12hrs later the drive was empty bar the system files, so i got straight to RockBox to see what options were available, and decided maybe 128gb SSD and new battery were the way to go.So i went through the steps as given on this site, altering original firmware backwards, RockBox installer, latest original firmware, the bit i am stuck on is changing to bootloader to 7pre4. What i need to know is where do i put the 7pre4 file to do the bootloader upgrade. I have draged and dropped it in to various locations on the player and i get a Checksums mismatch message when following instructions to do the upgrade?
I hope someone can help me please