My son's father and I are not together and I let him get his say on my sons name. I'm not happy with his first and middle names can I legally change it without input from his father?

How old is your son? Will this cause more problems than it is worth? In my opinion you may need to give a littlemore info. I mean if he has NO LEGAL RIGHTS to your son, you can change his name without his permission. Depending on the age of your son, this may not be a great idea.
Did his dad sign the birth certificate? If so, he lgally has rights to the child and you would have to have him waive his rights or agree to the name change.

Legal issues aside, you can call your child anything you want, regardless of his legal name.

It wouldn't be a good decision to change your sons name simply because you and their father are not together. When relationships don't work people tend to lash out and try to hurt the other person with the decisions they make for their child which causes more problems than necessary. You can call your son whatever you like without the technicalities of legal names.

my son's father and i are not together and i let him get his say on my sons name. i'm not happy with his first and middle names can i legally change it without input from his father?

No.
If you wish to change the name of your minor child, you will need to go through the court system to do so.You will also need to demonstrate that you have notified (or, if he is long gone, attempted to notify) the child’s natural father of your desire to change the child’s name. In some states, the natural father’s consent is required; in others, it is not. The court will weigh whether the name change is in the child’s best interests and will accept or deny the petition accordingly.

Some Courts adopted six factors. The first is the child's own preference. The second is the potential effect of the name change on the child's relationship to either parent. The third is the length of time the child has used a particular name. The fourth is the reputation or meaning associated with a particular name. The fifth is the difficulty the child may face as a result of either keeping the existing name or adopting the proposed one. The sixth, and last, is whether there has been parental misconduct or neglect.
A family court should always try to fashion any of their rulings to reduce any hostility and bitterness between any parents. It is important to emphasize to any mothers who are trying to change the surnames of their child, that an unhappy father who feels "dissed" is more likely to be a "deadbeat" dad. Consequently, a vindictive mother may encounter severe child support collection problems if she is ultimately successful in changing the surname of the child. Therefore, changing the surname of a child can very well be a "Pyrrhic" victory. The child's quality of life will certainly suffer if a mother's ability to collect child support is hindered.