Need help with UK mk3 focus

[ChloeSX]

Hey peeps, my friend has a mk3 focus and he wants to put an ST line diffuser on it, he said it came in 2 parts but he only needs 1 part of it [url]

|https://thumbsnap.com/hHMrhZ39[/url][url]

|https://thumbsnap.com/f7kc4EA2[/url]

He wants to know how to get it on basically (i dont know much about fords but i like cars, hence why he asked me)
Hes been told by someone that he needs to take his rear bumper off? and hes asking if he needs to buy any clips for it.
Any help would be much appreciated, thank you