My question involves name change laws in the State of: South Carolina

I have a 14 year old son and a 5 month old son. They both have there fathers last names. My 14 year old has been asking me to change his last name to my last name for the last few years. I ask a lawyer once before about this and he gave me some outrageous fee that I could not afford at the time. But i have been doing some research and was told that it's not as expensive as the lawyer made it seem. So my question is now what steps do I need to take to change my 14 year old last name? Also i have a 5 month old and i gave him his father last name but I now want to change it. I want both of my boys to carry my last name. My 14 year old wants nothing to do with his dad and my 5 month old father barely comes around. Please help me! I want to get this done as soon as possible. Thank you in advance!