How do I know what bit size an image is and how do I change it?

Look at the Document tab on top. RGB/8 for example. 8 is the "bit depth".

You change that under Image menu > Mode.

Hi Michael,

Just to confirm, I believe you are referring to the bit depth of the image that you are working with, right?

If so, you can check and change the bit depth by going to the Image menu in Photoshop > select Mode and change the bit depth. The option that you with a check mark would be the option which is currently selected for the image.

Regards

Nikunj