A basic search would give you many answers to accomplish this.
Depending on your system you can use one of the suggested solutions here: https://www.makeuseof.com/how-to-make-b ... ansparent/

If you only have a single image you want to convert there are many online sites where you can do easily this for free.

I always use GIMP. Basicly you add and aphachannel to the image and set the transparency to a selected color. The link I gave also explains how to remove a background for an image using different graphics programs.

Remember to save in a format that supports transparency, for example PNG. (JPG doesn't support transparency.)