upgrading from kentico 6 to kentico 10

Yes, but not directly from 6 to 10. You have to go through each upgrade between those two: 6 -> 7 -> 8 -> 8.1 -> 8.2 -> 9 -> 10.

Hassan, it's always possible, but the truth is is it worth it?

V6 means the site is 5+ years old, do you really want to spend all the effort to upgrade an old design and implementation to the latest? What do you gain from that? Only the basic functions that was available back in V6. All the new features still need new implementations.

Our typical recommendation for clients that have a site running on V7 or earlier is to consider redesign and implementation with the latest version.

As both Roman and Rui have stated it is possible but as Rui indicates, you're best bet is to really evaluate if the expense associated with performing 6 upgrades vs. starting with a fresh copy of v10 and move your v6 content and design to v10. We do this kind of evaluation all the time. Look me up if you need any assistance.

If most of your website is Out of the box it will be a lot simpler however if you've any custom components than you will have to keep upgrading those components at every level to make sure they are the right input for the next upgrade level.

This will be true for Macros too. In short performing upgrade from 6 to 10 step by step as Roman said will be too painful and will result in nothing concrete.

Web sites usually have 2-3 years of life cycle. You already need a makeover to match little closer to what current standards are.

Let me know if you would like to discuss it any further

Thanks, Chetan