How to move Magento Customer, Order and invoice from lower version to upper version

We have upgraded a Magento website from 1.8.0 to the Magento ver. and we have taken 2-3 days because website has a lot of the products and customer and it is making good amount of orders per day so our main issue was we can not down the

Magento 1.3.x, 1.4.x, 1.5.x, 1.6.x, 1.7.x, 1.8.x and 1.9.x upgrade process by using the SSH.

There are many features added in the latest versions of the Magento, such as the responsive web design, making the site a perfect fit for mobile devices, Improved speed, performance, security and checkout process and may other functionality, so it is very important to upgrade the Magento Version from

Customer Can Not Login After Magento Upgrade

Yesterday, I have done a Magento upgrade from Magento version 1.7+ to Magento version 1.8+ for one of our client, Everything was fine and working well in the admin panel but there was some problem on the frontend user login form. I was trying to login from my user