Magento is going forward to satisfy both customers’ behavior and e-merchant’s need. Magento 1.9 is last version of Magento 1.x with supported features such as financing and payment solutions, security and UX, cross-border price consistency. In Nov 2015, Magento released Magento 2 – the next generation of Magento and e-commerce platform. Magento improves this version with important change that proves Magento is one of the professional shopping cart. There are many radical change in structure. Magento 2 uses command line for development.

As I understand, many storeowners update old version of Magento to Magento 2. It is not really an upgrade magento 1 to 2. It called a Magento migration to migrate data from magento 1 to magento 2. People can see some suggestion to upgrade to magento 2.

However, in some case, the migration process is not successful. It hides risks of data loss, site break down, cloud connect fail. When you clear the cache and hit the url its infinite redirect loop. Upgrading through the browser has a number of downsides, most notably that the browser can timeout or anything from the web server you’re talking to and the php backend. When that happens you have no clue what went wrong or is going to go wrong.

Online business can try with Magento 2 migration tool that is an automated solution of LitExtesion to migrate database from magento 1.x to magento 2. Although Magento releases Magento 2.2, Magento 2.0 is the most popular version of Magento 2. See the detailed information:

If you are a loyal user of Magento 1.8.1, Magento 2.0 is a smart choice for online business. You can upgrade magento 1.8 to 2.0 automatically with Magento 2 upgrade.

Magento 2 upgrade is developed to support users to migrate data from all version of Magento 1 to Magento 2 including Magento 2.0, 2.1 and 2.2.

Hope that this way can helps you to solve your problem to upgrade Magento 1.8.1 to 2.0.

Source: Update new trend to upgrade Magento 1 to 2