There's much said about resizing, about which method works best and how to go about getting as good a result as possible. But PS seems as good as any:
Image
Image Resize
Set to percent: anywhere from 200-400 (depending on original - experiment to find optimum)
Constrain Proportions, Resample Image should both be ticked and latter set to Bicubic
Save file as a TIFF (which is where large size comes from - no compression)
HTH - and a good w/e to you too!
