How do i get my remote key to work please?

I have just bought a 2003 ford focus, I have one key which starts the car and locks the door manually, but it looks nothing like the picture in the frd manual, and the battery is different to the one specified in the book. The other key (half a key has no remote bit but is the one that opns the bonnet) I am assumin this orginally was the master, Can I get my key that I am using to become remote again, so I dont have to struggle with locks everytime?

Thanks V Much