how to pick resolution?

[TeKett]

Waifu2x-extensuion-gui is the only gui that has resolution option (both custom scale and exact resolution), but don't feel like paying for it if i could just use this directly. My goal is not to upscale TV anime, but booru images. But i dont want to always upscale, but sometimes only us it as 1x to remove grain/artefacts, since people love to upload 4k images with jpg size of 100kb.