When you do not close the unnecessary apps on your phone, they take up RAM. so to free up RAM, all you need to do is close the apps. You can either close the apps one by one or follow the below steps to close them all at once and free up RAM on your device:
Launch Recents on your phone by long-pressing the home button or tapping the menu one.
From the list of apps, swipe the app windows to close them or tap the cross button on the bottom.
Once you close all the apps, you will get more RAM space for other purposes. You can download the best phone cleaner app for android listed above to free up the maximum storage out of your device.