Image size i.e.pixel dimensions and file size i.e. MB are two different things.
To achieve a target file size, use Export - Save for Web(legacy) and set it to jpeg. Then adjust the quality slider whilst watching the file size at the bottom of the preview.
Thank you this is helpful, I am not sure of the the JPEG size to set it to
at the moment. (I am more of a hands on artist)
Kind regards Nsrus
The pixel dimensions depend what the jpeg is for. Is it to be viewed on a screen, or printed and if so how big is the final print. If you know the current pixel size and how big the physical print size has to be (cm or inches) then we can advise you further.