Hello Amar,

from 4.6.9 to 4.7 you can use the update package (K2 Update Package 4.7 (4.16060.2000.2)) instead of the installer (K2 Installation Package 4.7 (4.16060.2000.2)) . I have seen issues with the instaler on older versions, but did not have issues this time with the update package. I have done the update from 4.6.10 to 4.7 on a test system and have not found issues until now, but testing is ongoing.
Please take note there is a lot of 3rd party software which is no longer supported (https://help.k2.com/news/4.7technologies). For the Sharepoint 2010 smartobjects i can say the smartobjects are not gone after the update and they are still functional at our test system... but not officially supported. Also K2 changed behavior in API, if you are using custom code you should look into that as well. For example this part (https://help.k2.com/kb001745):
 
The Workflow Management API behavior has changed. Methods that return lists were updated to return only the data that the currently-connected user has rights for. If the user does not have any rights, an exception is no longer thrown, but instead an empty list is returned. If you have code that relies on an exception to be thrown on these management methods, you will need to change your code accordingly to cater for the change in behavior.
 
So if you go to 4.6.11 you will have support for those old software versions until September, under 4.7 i am not sure how support handles support requests if you have old stuff in your environment.