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.
As I said you can view or change the resolution in Preview's Tools.
Be aware though that Pages often misreads the native resolution, which will change anyway if you rescale the image inside Pages. Halve the size in Pages and you double the resolution and vice versa.