How Do I Reduce Image Dimensions?
Reduce the width and height in pixels with a resize operation. Keep the aspect ratio unless you intentionally need a non-proportional crop or distortion.
What to do
Choose the dimensions required by the destination. Avoid reducing a large original repeatedly; create the desired delivery size from the original when possible. The simplest next step is to Resize Image. If the issue is actually about image size checker, see Image Size Checker as well.
Why this happens
Image problems often come from three separate variables: pixel dimensions, encoded file size and file format. Changing one does not automatically solve the others. A very large photo may need resizing even when its format is already JPG; a transparent graphic may need PNG or WebP even when the file size is acceptable; and an upload limit may be measured in megabytes rather than pixels.
Before editing, check the requirements of the place where the image will be used. That gives you a concrete target and reduces unnecessary quality loss. When possible, keep the original file and create a delivery copy for the specific destination.
Common questions
Does reducing dimensions reduce file size?
Usually, because the output contains fewer pixels.
How do I avoid stretching?
Keep the aspect ratio locked and change one dimension at a time.
Should I resize before compression?
When the image is oversized, resizing first is usually a sensible workflow.