I currently have Ubuntu 15.10 and I want to upgrade that to Xenial Xerus ( 16.04 LTS ),

I invoked this in terminal :

update-manager -d

but when the windows pops out and it downloads some files from repository it says :

The software on this computer is up to date and it doesn't find the new release

What am i missing?

I currently have Ubuntu 15.10 and I want to upgrade that to Xenial Xerus ( 16.04 LTS ),

I invoked this in terminal :

update-manager -d

but when the windows pops out and it downloads some files from repository it says :

The software on this computer is up to date

It doesn't find the new release

What am I missing?