In some cases, there may be genetic factors at play and there is little you can do to change your appearance. Other situations involve a dominant side-effect where the side of the body you favor may be stimulated to grow more muscle. You may be able to correct this asymmetry by adding an extra set to the smaller body parts. Utilizing dumbbells instead of barbells when able can help as well.

If you are a beginner (exercising for at least 2 years consistently or less) it may just be a matter of time before everything evens out. As long as you are eating and hydrating properly the smaller body parts should grow to match the dominant side.