Does anyone know how I can change the size of the images on the search page?

For an online store

All you can do with images by code (api), you will find here…
https://www.wix.com/velo/reference/$w/image

The only given way by wix/velo is the “fitMode” to change modify somehow images.
https://www.wix.com/velo/reference/$w/image/fitmode

But you surely also could use an html-component or an custom element, to achieve your aim, but this would be a difficult workaround (surely not for beginner).