How do you all make your UK general election maps?

Hi there! I'm an amateur imaginary elections maker, but I've struggled with making UK general election maps for some time now. I use Paint.Net so that might have something to do with it, but I have to convert the maps from svg to png, and then put it in, and then it's basically impossible, lest I go in and individually clean up every constituency, to get a result with any ease. For those with this experience, could you advise me?