Hi
Welcome to communities.
please let me answer to your question i.e if any one faced any problem time of upgradation ,
it is little tough to say because time of
up gradation we might face different problem and its not possible list of all the problem
so please take pre requisite and stat upgrading
2nd how to upgrade , below link will help you lot
http://www.vmwarearena.com/2014/01/vsphere-distributed-switch-part-12.html