Hi, whenever I try to install act of war I get a message saying that installer files can't be found and I have to shut down the installer.

Anyone have a solution?

The installer comes in two parts, more specifically two separate files. Both these files must be placed in the same directory before the executable is launched. If you have already downloaded both files, try moving them to a new directory, for example 'c:\aow_install', then launch the installer.

If you still can't figure it out I recommend using GOG Galaxy. Similar to Steam, it helps you download and install games with just one click.

Additionally, make sure none of the files have been renamed.

I've downloaded both files for High Treason, but when it prompts me to find the second file and I select it, it simply says "this cannot be installed without the required file, Cancel?", and if I choose not to cancel the installation it just shunts me back to the file select screen no matter which file I choose. and when I try to play it through GoG Galaxy it doesn't launch.

Not entirely sure what's going on

If you install manually the .rar files need to be renamed to .bin

All GOG windows installer files have either the .bin or .exe extension to begin with. All one should have to do is: 1.) make sure to download any and all pieces of the installer (an ".exe" and often one or more ".bin"s); 2.) make sure everything is in one folder together -- and nothing has been renamed from what it was downloaded as -- before running the .exe of the installer; 3.) ???; 4.) Pr...err, play the game!

Well mine were .rar for some reason except the installer, that was an .exe.

The only way they could've been .rar is if someone changed the file extension after they were downloaded. It's more likely just a case of you having the .bin file extension in Windows associated with a program that treats files of that type as compressed archives which can just be easily "unzipped" (like .zip or .rar) -- which, to be fair, I think they sometimes are, but never in the case of GOG games.
By default, Windows hides the actual file extension in File Explorer (at least in Win 8 & older -- not sure about Windows 10), but you can make file extensions visible by changing a viewing option in Windows File Explorer. (There are other ways to see the file type even without doing this, too.)

FYI, some versions of IE helpfully renamed the .bin files to .rar (as the .bins are .rar files) during the download (technically before it started writing the file to disk). IIRC, some download managers can also be "helpful" in this regard.

Well, I stand corrected. (Sadly, not knowing this is just part of the price I pay for not using Internet Explorer.) =)