you 'can' do what you want in Adobe, but they sure make it complicated...*grin*...you open Adobe..click on "get & fix photo" then click 'file open'...and find the picture you want. Then choose the size (as in 50% of the original)..however, *if* you wish to crop (they call it trim), you should do that first.You click on trim, then choose 'any size' in the box and draw a box with the cursor around the part you want and click 'done'. Then see how big it is...at the bottom of the pic, it says it is "x" inches by "y" inches and lists the byte size..5x7 is a good size...under 80,000 bytes is ok usually, but smaller is possible.

all this is much easier in some programs, but Adobe is oriented toward commercial sizing and printing and 'leads' you to standard settings...

(you 'might' make a copy first to play with, and just mess about...