What for?
What evidence do you have that:
(a) fragmentation is giving you some sort of problem, and:
(b) defragmenting is going to fix it?
In particular, what will you measure, before and after, in order to confirm that what you did was useful?
If the answer to all these questions is "don't know" or "some bloke I met in a pub told me to do this" or "I read it on a web site so it must be true" then I suggest you spend the time doing something more interesting instead.