upgrade exchange 2013 cumulative 15 to cumulative 21
i need expert advice to now what i need to do to install exchange 2013 cumulative update 21 from exchange 2013 cu 15 installed.
i am on windows 2012 r2 with 9 server exchange 2013 cu15 and .net framework 4.5.1 (the relaese on registry indicate 378675).
can some one tell me what are the road to upgrade to Cumulative 21?
1- are update active directory schéma is needed?
2-what are the prerequisites
3- are higher .net framework version is needed (actually 4.5.1 on server)