Make background of a pattern transparent

Hi.

I have accquired a license for the image above and I want to remove the red entirely, and make the background transparent. I want to only end up with a black and white pattern on a transparent background, so I can then put the transparent image on to any color background I like.

So far, instead of trying to create a transparent background, I tried replacing the background color to navy blue for example, but that ended up with faint red lines from the original which didn't match the color I replaced. So from there I went back to this original file, and converted it to b&w. The idea behind that was that all of the color on the image would be converted to grey scale, I would then replace the grey background to whatever color I wanted the background to be, and the leftover lines that were red in the first example wouldn't matter as they'd be in greyscale and either invisible or barely detectable, unlike the red lines that were showing up on my navy blue background. However, this didn't work. Once I changed to b&w, I lost the ability to replace the color, or rather, I had the ability to replace the color, even the preview would show the correct example, but once you confirm the change, the image stays in grey scale. Can someone please help me?

Ideally I would like a transparent background.

Thank you,