Changing black colours in jpegs

Hi everyone, I need assistance, the designers that I've been using have closed up their shops and have left me without artwork. All I want to do is change the colour of the black in the attached image to a light gray, I spent a few hours yesterday on google but I couldn't really find something that gave me the desired effect, the black just doesn't seem to change. I've tried using masks, layering images and just removing the black back ground and tried making a new object with whatever colour I want but I can't get the effect I'm looking for.  Apologies if this seems a bit vague