Short answer, you don't...
Moving from Magento 1.x to 2.x is a process, not an upgrade.
The database schema changes so much that the process is referred to as Migration. The data has to be exported, translated to the new database tables/columns or discarded as applicable.
The directory structure and internal operations of Magento have changed so much that you will need to check with your developers to get modules rewritten to work with Magento 2.0. Same goes for themes and templates.
Basically, you will be running the old 1.x version on your live site while you move your data to the 2.x version running on a development test server and function testing until you think it's ready for real world use.
I am also interested in knowing proper procedure for upgrading to magento2 and as well as would like to know do i need to make any changes to the extensions i am using or would they be automatically upgraded or is there any tool for it.
As your site will already be live so you need to have proper planning and strategy before upgrading your site. You need to pre-analyze the complexity you will be facing during site migration and how can you resolve it.
Magento 2 is totally refreshed and based on latest technologies, so before installing or upgrading Magento 2 on your server, you need to check the server requirements and upgrade it accordingly so that the server meets all the requirements as specified by Magento to install Magento 2.
You can visit the following link : http://devdocs.magento.com/guides/v2.0/install-gde/system-requirements.html
Most of the stores have 3rd party extensions so if you are planning to migrate to Magento 2 you need to either get all extensions from your extension provider or we can create all those extensions for you which will be paid
Note - Backup your db properly so that old data can be migrated properly but expert advice is needed for this on how to migrate data
For more details : Migrate from Magento 1.0 to Magento 2.0
Whenever I see no upgrade path for a product this puts me off using it. The lack of themes for 2.x is also a concern.
WHEN AND WHY SHOULD YOU UPGRADE TO MAGENTO 2.X?
It’s been more than a year now since the Magento 2 series got launched. The GA version of Magento 2 launched in November 2015. Magento will most likely quit supporting the 1.x Enterprise Editions in November 2018.
1. When should you upgrade to Magento 2.x?
If you are a very small business operating on Magento with relatively less amount of customizations, migration to Magento 2.x will take a couple of months. So you can consider upgrading as late as Jan 2018.
If you are a mid-sized business with some hundred SKUs and a moderate amount of custom work done on the store, you should start your upgradation by mid-June this year. It will roughly take 3-4 months to migrate, get all the custom work re-done and have a perfectly streamlined store.
2. Why should you upgrade to Magento 2.x?
Figures like 50% faster load time and 38% faster check out in comparison to 1.x series mean a huge leap ahead. With proper hosting setup, it can now deliver nearly instant server response times for catalog browsing. Magento 2.x can manage 10 million catalogue page views an hour compared to only 500,000 page views per hour as supported by the Magento 1.9 or Magento 1.14 platform.
The new admin interface has a fluidic and interactive design which is far more user-friendly than that of its previous generation. Due to the intuitive back-end UI merchants can now open up the admin panel from any touch based device. Though the backend is not completely responsive but its far easier to use than the previous version.
Read the full article here: When and Why should you upgrade to Magento 2.x?