9.2.1.9 to 11.1 if it isn't broke........

have been using 9.2.1.9 on a 8GB USB as a file server only for the past couple of years.  i have downloaded the 11.1 iso but as i am a 'if it isn't broke don't fix it' person am having second thoughts about updating.

can i do a straight forward update with my version of freenas via the GUI?
Is the 8GB USB with 9.2.1.9 installed enough space for the upgrade to 11.1?
Any good reasons to/not upgrade?

appreciate any advice