Selenium 2 to
selenium 3.0.1 is bit easy take less effort
One of the biggest change is that the old Selenium Core libraries will be dropped in 3.0. The focus will shift completely to the WebDriver API.
For the last six years it has been advised to switch to the newer WebDriver APIs and to stop using the original RC APIs. With Selenium 3.0, the original implementation of RC has been removed, replaced by one that sits on top of WebDriver. For many users, this change will go completely unnoticed, as they’re no longer using the RC APIs.
Firefox is only fully supported at
version 47.0.1 or earlier. Support
for later versions of firefox is provided by
geckodriver, which is
based on the evolving W3C WebDriver spec, and uses the wire protocol
in that spec, which is liable to change without notice.
WebDriver API has grown to be relevant outside of Selenium. It is used in multiple tools for automation. For example, it's used heavily in mobile testing through tools such as Appium and iOS Driver. The W3C standard will encourage compatibility across different software implementations of the WebDriver API.
W3C Working Draft
There are many updates please have a look