If it helps, you have to manually copy and paste the new contents of *each* itch.io patch for PC after v.4.51c, and the patches *can't* be "stacked in" and copied all at once, together -- that's where I got errors.
So, after you play to the end of chapter 4, you unzip 6.1 to your hard drive in its own folder, then copy and paste the files in 6.1 to your original 4.51 folder, overwriting when prompted. Then you play through chapters 5 & 6.
After you're done playing to the end of chapter 6, then you unzip patch 7.0 onto your hard drive in its own folder, and (reverse the process) copy parts of your current game into the 7.0 folder -- the listing here for patch 7.0 on itch.io has notes on this, plus a pic showing you which specific files to copy over. Then, you play through chapter 7 from the 7.0 game folder's LeapofFaith.exe.
Yeah, it's a really clunky patch process, but I guess that's the trade-off for getting the game for free/cheap on itch.io. The game is for sale on Steam now, for anyone who would rather pay more for a standard patching process.
Renpy puts its game saves in the Users/Owner/AppData/Roaming folder on your hard drive -- separate from the games themselves -- so your saves should be there if you want to copy them somewhere else as "emergency backups" or whatnot. Good luck!