Before starting the method,your android device must be rooted.
To root your android device open this link widlon/rooting
You should also check the compatibility of this app with your device.If it is not compatible with your device then you can download other similar apps.
So lets start with the method-
1- You should have a good connectivity of internet.
2- First of all, Open Google Play store on your device.
3-You need to download a application named as ROEHSOFT RAM EXPANDER from Google playstore.
4- Open the app and run it.
5-It will increase the RAM of your device by using the free space in your SD card.
So these were the simple steps to increase the Ram of your device.