if you are looking at a far away object, your eyes don’t need to refract the light too much in order to focus it onto the retina. So in this case the lens shape should be flat instead of fat. And how this happens is that ciliary muscles relax, and this cause the elastic fibres that act on the lens to become tense and pulls the lens making it thin. For a near image, the opposite would happen, with the ciliary muscles contracting and the elastic fibres becoming loose so the lens becomes fat, as it has to refract the light more to focus it on the back of the retina