demopalette.jsx that comes with AE has scale comps/layers/cameras and keyframes
some tips:
1.turn on collapse transformations
2. try not to stretch when rendering with pre-fielded footage
3. for best quality, pictures should be pre-bicubic scaled in photoshop
Now if you just want to resize comps/layers but leave everything else alone, I made a script for that too.
Located in Free scripts at my website that scales all highlighted comps and layers in project to exact pixels sizes and aspect ratio. There’s also anchorepair script in case some comps need a reset anchorpoint.
https://technicolorsoftware.hostzi.com/