That is a bad title and a really vague question.
Upload to where?
Or do you just mean you have to insert an image into Pages?
You can set the resolution and crop the image in Preview.app. I assume you have the photo somewhere either on your camera or in iPhoto. Find it and copy or drag it into/on Preview:
Menu > Tools > Adjust Size…
When you have it the way you want it, either Copy/Paste or Save/Drag it into Pages.