upgrade version

can i upgrade my current version of unity 2.6 to unity 3.0?

if its possible then how?

Yes, but it's a paid upgrade. Go to the Store page on the Unity, enter your 2.6 serial number and choose upgrade. The prices will change automagically.

https://store.unity3d.com/shop/

If it's the free version, just download and run the new 3.0 file and it will do all the work.