Resize Website Graphic Height

I have a single graphic that sits on my website and I simply need its height adjusted so it displays correctly across modern browsers and screen sizes. The file itself is ready to hand over; I just need the updated version returned to me at the new height while keeping quality intact and the width proportional, so there’s no distortion. Once I receive the resized image, I’ll upload it myself and confirm everything looks right. This is a quick, one-off task; as soon as the new file is delivered in the same format as the original (plus a web-optimised PNG or JPEG if different), the job is complete.