Just visit the Malaysian Examination Syndicate website, maybe through googling Lembaga Peperiksaan Malaysia.. There'll be a tab on SPM (U) where the (U) would represent Ulangan. Through that tab, you'll have all the official information on the schedule, the pre-requisite to sitting the examinations and all that comes with it.. You can even download the application form in pdf format. Since it's the Examination Syndicate, all informations are official and more updated than even the Ministry of Education themselves.
Feel free to email them on any doubts that come to mind, but be wary that the reply will only come after a week or so. I'll hyperlink the files when I have access to a desktop.
Regarding re-take SPM