Yes you can. You may want to investigate the reasons as to why retention was suggested. Usually a child can be brought on level or higher with some help through the summer. I would find your child's weak areas and work with he or she through the summer.
Certainly! Perhaps the question to ask is, "How will retaining my child benefit him/her in the future?" With an answer from your child's teacher and principal you can better assess whether retention is an option for you and your child.