Help mysql delete from an array

OK, I have this rating system on my website, and the php refers to a database, to check recorded IPs, so no-one can vote twice. In the database, the IPs are stored under a used_ip column, in an array. I have attached a picture. The table name is rating. How, using mysql, can I delete specific IPs from that array, without deleting the entire row??

Thanks in advance.