How do I change the title....

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HOw do I change the title to my car? I live in the US, texas. My dad co-singed for me, but was put as the buyer and me as the co-buyer. The car bills came in both his and my name. He died a year ago and when i went to go renew my insurance they asked if the car was mine, technically it's not, so I said no and they suggested that I change it to my name. Please help. Will it cost anything.