Remote Diagnostic Agent (RDA) 4.28 was released on 12th June. Full details can be found in this My Oracle Support document

RDA 4 Release Notes [ID 414970.1]

From a Fusion Middleware Core Component, Install and Administration perspective this latest release does not offer any significant new features or changes. However, despite the lack of Fusion Middleware specific new features in version 4.28, Remote Diagnostic Agent still comes as highly recommended. It is incredibly useful problem solving / troubleshooting aid. Support engineers dealing with Service Requests often request RDA output as it collects just about everything you might need to get a view of the state and configuration of the host operating system, network setup and Fusion Middleware components. To find out more take a look at

• Running RDA Against Oracle Fusion Middleware 11g [ID 853437.1]
• Getting Started With Remote Diagnostic Agent: Case Study - Oracle WebLogic Server (Video) [ID 1262157.1]

Note: While the latter document looks at RDA from the perspective of WebLogic Server, much of the advice given in the videos can be applied to other Fusion Middleware products.

Ok, let's get back on track with the topic suggested by the title. If you are already familiar with Remote Diagnostic Agent you may ask the question - 'How do I keep my RDA at the latest version?'

The answer is in "Running RDA Against Oracle Fusion Middleware 11g [ID 853437.1]". To quote:

There are two methods:

1. Upgrade RDA via OCM (Oracle Configuration Manager) 
Refer to the advice given in:

Remote Diagnostic Agent (RDA) Upgrade README [ID 1309034.1] 

OR

2. Manually download and upgrade to the latest version. 
To quote from

Remote Diagnostic Agent (RDA) 4 - FAQ [ID 330363.1]

+++++++++++++++++++++++++++++++++++++++++++++++++++++++
How do I upgrade my RDA 4.x installation from the prior release?

The most simplest and reliable way to upgrade your RDA installation is 
delete or move your old installation  to a new location. Then install the 
new release into the location you had the prior release installed. 

If you want to reuse you old setup.cfg file, you can place the older version 
into the new <rda> directory and it will try to upgrade your setup.cfg 
to the new features.

A second approach is to install the latest RDA into another directory, 
then if needed copy the old setup.cfg file to the new RDA directory. 
When the new RDA is run for the first time, it will try to upgrade 
your setup.cfg to the new features.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++ 

The upgrade method via Oracle Configuration Manager is nice because it allows RDA to be auto updated whenever a new release of RDA is made available (which roughly speaking is every 3 months). However, it does require you to install and configure Oracle Configuration Manager in addition to RDA. A quick guide to Fusion Middleware 11g and OCM can be found in this support document.

Configuring OCM in Oracle Fusion Middleware 11g? A Quick and Easy Guide [ID 1096871.1]