as the dialog telling you that you do not have enough room to install.
Check under USAGE where you will find a list of what is on your phone.
From there you delete whatever you want.
I took out a subscription with Match some months ago. It synched with my 64gb iPad 2 without problems, taking away all the previously stored 38gb or so of music and freeing back up that space on the device. However, it's not done so with my iPhone 4s. It seems to be playing the music from the cloud OK, but the 38gb of internal memory is still shown as used for music. Now I can't upgrade to iOS 8 as I'm being told my iPhone doesn't have enough memory left (there are other things on there besides the music). How do I force the removal of the music on the device to free up internal memory?