As we know there are three challenges in the blockchain. i.e
Right now, ethereum working is based on proof of work. The most advantage of PoW is more secure, more decentralized but it is the rising cost of energy it takes to maintain network security. The Bitcoin blockchain requires consequence power, greater than the power output of many nations, to remain secure and operate in-line with its mission. Ethereum founder Vitalik Buterin and other key network developers noticed this problem and determined PoS is a viable alternative to this energy consumption, hence ethereum move from PoW to PoS. Even though from PoW to PoS they will not hit all these three challenges, maybe it is most scalable but less decentralize or less secure. So how that approach hit these three goals. For that, they are using etherum 2.0 concept.
Here is a description of basic ethereum upgrade network
How Ethereum is mined becon and Casper refer solutions for switching. This addresses how new coins are created and how the system is secured.
In general divide a large database into smaller having the same general concept with more manageable parts, for the Ethereum network. This addresses issues of transaction speed and scalability and stops one app from slow down the network.
It allows executing code faster among other things. It enlarges the capabilities and the coding option for the Ethereum Virtual Machine.
It is an extra layer that sits on top of the network that can handle huge amounts of transactions. It is the version of ethereum Bitcoin's Lightning Network.
It is off chain scaling solution, like Plasma. Thus, this is a solution for Ethereum to the Lightning Network.
Ethereum's Serenity upgrade will bring Proof of Stake, Sharding, a new virtual machine (eWASM) and more. It's important to understand that this upgrade will not take place at a single point in time - instead, it will be rolled out in phases. The entire upgrade is very complex and is currently being carried out in phases over a number of years. The final completion date is set in 2021. The upgrade of Serenity is broken down into 4 phases, each of these further divided into sub-phases. The first phase, is Frontier, was Ehereum's initial build at launch. The second phase, Homestead, took us into 2018. The third phase, which is the phase we are currently in, is called Metropolis. Metropolis consists of Byzantium and Constantinople, of 2 hard forks, the latter of which has been delayed until late February due to passiveness in its code. So we are still in the Metropolis stage, we have begun the initial stages of the 4th phase, Serenity.
Serenity (Ethereum 2.0) is the most feature-rich stage and important of Ethereum's development that gear a variety of issues from economic finality, scalability, and security.
Every feature of "Ethereum 2.0" offers an answer to the above problems... and it reminds us of that bright future. Ethereum 3.0, 4.0, etc are possible for the future ( Ethereum can evolve too, but there is no one says development ends there). Apart from other blockchain designs these goals or principle are sets Ethereum 2.0.