No worries at all
You don’t need to download both versions of the game. Just pick one version that works for your system.
If you're using a low-end PC, the DX11 version (Part 1 & Part 2) is recommended. Make sure both parts are in the same folder before extracting.
The files ending in .z01 and .zip are an alternative version bundled specifically for users who can’t extract .rar files. These are DX12, just a different compression format for convenience.