Open Question: i'd like to obtaine an engligh high school diploma?

i'm 18 and i'm italian,and i want to do the university in uk.actually i'm in italian high school in italy,but in italy this school finish at 19!! is it true choose a type of exams to do in uk?not all the subjects but only the candidate wants.what type of exams i'll do?furthermore i can't go to uk,but i can do the exams on-line?i found this link(http://www.cie.org.uk/qualifications/...) but my pc doesn't show to me!! plese write me soon by e-mails.thanks. it's very urgent!! i'm very desperate because i don't know how to realize my plan and nobady help me!!!