4G refers to the higher spectrum of the connectivity. It offers the same set of features like previous technologies like 2G and 3G. However the speed at which these services delivered makes the different. For example, the data being sent by the 4G is at much faster speed. This makes it easier for the network to be used for watching live streaming sports, movies, shows etc. Also the speed such as this can be good for the video conferencing too. It can simultaneously be used for the data and voice at the same time.
If your smartphone supports 4G LTE then and only then you can upgrade to such service. If your smartphone number and the SIM is still at the 2G then you may have to upgrade. The reason being the nanoSIM and also the IMEI code being sent at LTE towers is lot different. Airtel, Idea, Vodafone, Reliance and Tata are the top 4G providers.
The current networks are going to be switching to the 4G technology eventually, so in future you are going to upgrade to it too.