I still get questions on how to find EM13 Release Updates, as they seem to be a bit hard to find..
Let me give you an example of searching for RU14, that came available some days ago.
Connect to the My Oracle Support website https://support.oracle.com using you personal account.
Navigate to the Patches & Updates tab
Select Enterprise Manager Base Platform for Product
and for Release is one of Enterprise Manager 126.96.36.199.0 and Enterprise Manager Agent 188.8.131.52.0
and press [Search]
Notice RU14 for OMS and Agent, as well as OMSPATCHER release 13.5 are highlighted and can now be downloaded.