Check out step 9 in this guide, please forgive me if this seems amateur but I do not know your level of experience.
What do you see when you reach step 9 on your system, does the partition say unallocated space, or is there already an existing partition? If there is one that already exist you need to select it, hit advanced, and delete it. If prompted with whether you want to do a quick or full format, choose quick because you do not want to use up unnecessary writes on your SSD.
EDIT -- If you have additional hard drives installed with data you do not want to lose be sure of which partition belongs to which disk other wise you might erase all your stored data.