serpentine belt replacement 1.6 petrol berlingo

i have a 2005 1.6 petrol berlingo no air con, i need to replace the power steering belt,  how do you slacken off the tension and do you need to remove the engine mount bracket to do it to get access to the pulleys.

the belt the shop gave me is a  6PK 1453

any advice greatly appreciated as looks a bit complicated as not able to see the alternator clearly

many thanks