G: It seems the OP isn't familiar with cropping in LR, PS, Camera Raw, etc.
OP: When you select a crop tool, you can choose what aspect ratio you want to generate either by right clicking (in Adobe Camera Raw,) or from the respective menus in Photoshop and Lightroom. This assumes of course that you are editing with Adobe CC apps. However, other image editors will have a similar procedure, I'm just not familiar with them.
Now, if you left click and drag, you will see a selection begin to appear and it will be in the aspect ratio that you chose. Start by just creating a selection smaller than your image. Then, left click the center and move it to the top left corner of the image. Next, hover over the lower right corner of the selection until you get the diagonal arrow and drag that point to the bottom edge of your image. Finally, left click in the center of the selection and move it over the area you want to keep from the image and hit <Enter>. That will give you the crop you need with no distortion. This is different than what you're thinking, i.e., to try and adjust the dimensions of a 16:9 or 3:2 image which WILL distort the photo.
Holler back if you still aren't sure how to do it.
KB