Steam – Nvidia Optimus Not letting me start games

Have you been using many mods? Some are known to leave garbage data in saves that slows the game down after the mod has been updated or removed. Try starting a new game with 0 mods and see if the slowdowns continue.

Also, make sure your mods are compatible with the version you're running.

You say you don't know how to edit the .ini files – unfortunately, to fix this you're going to have to learn. This is a common bug and the solution is to

1. Make the changes directly to the INI files
2. Set them read-only (right click → properties) so the changes won't be undone

You'll find the INI files in a Homefront folder under My Documents/My Games. They're just text files, so open them up in your favourite text editor (not a word processor like MS Word) and make the changes. You just find the field you want to change, then change whatever is after the = sign. The graphics settings you're looking for should all be under one section – sections are started with a title between square brakets (e.g., []). When you tweak the setting, remember to unset read-only first and set it read-only again after.

Homefront has multiple INI files for configuring different things. For graphics you'll want to look at GCEngine.ini. If you want to tweak mouse input, for example, you'll look instead at GCInput.ini.

It's easy once you actually start looking in the files, though it may take some time to read through all the fields and get an idea of what does what. The best way to learn is to just change things that look likely, and see what happens – that's how all the tweak guides were written. Just make backups of the original INIs before you start tweaking, and you have nothing to fear.

There are lots of discussions on INI tweaks for Homefront, such as this set of performance tweaks or this other Homefront tweak guide. Reading those will give you a sense of how and what to change.

As an alternative to a text editor, you can use a program like INI Settings Editor to give you a graphical interface to the INI sections and fields.