App Store sometimes can't install apps, iCloud icon appearing instead of INSTALL icon
An iCloud icon means that you have bought this application before and this is the only different between showing this icon and GET/INSTALL icon.

You can not change the iCloud icon because it is bought and it can't be undone. If you are unable to get the application, maybe there are network issues. Try change the network you are connected to a more reliable network, and reboot your device.