Q: How to adjust setting on 9.7" ipad pro to take higher resolution photos?

Where do you see 240 x 320 resolution? Pro 9.7" camera is 12/5 megapixel (rear/front). That resolution does not look right.

You probably email the thumbnail instead of the entire photo. Try copying the photos directly with lightning to USB cable connected to your iMac. You should get the real size (12 Megapixel) instead of smaller/resized photo sent by email.

When you send as an eMail from the iPad you are given the option to change the file size (resolution). You appear to have sent it at the lowest possible size. Try resending and leave the setting at "Actual Size"

Instead of emailing the pic to your iMac, you could easily just airdrop it - much quicker and easier. This was a pic I took:

And here is the info on it:

It is larger than my 27" iMac screen. That is the native mode from the iPad Pro 9.7".