Remember that any unallocated space after the partition is available for use. Even if you couldn't shrink from 51G to 45G with the available 10G, which even by my lamentable arithmetical powers would seem to be possible with 4G left over, then you should still have sufficient space on the whole disk--about 13G--for your Yosemite install.
Anyway, give it a try and find out. The very worst that can happen is that you make a mistake and lose all your data. Hopefully, it doesn't come to that ... -- You received this message because you are subscribed to the Google Groups "MacVisionaries" group. To unsubscribe from this group and stop receiving emails from it, send an email to macvisionaries+unsubscr...@googlegroups.com. To post to this group, send email to macvisionaries@googlegroups.com. Visit this group at http://groups.google.com/group/macvisionaries. For more options, visit https://groups.google.com/d/optout.
