"There is insufficient space on the device"--This is not duplicate
It's not about how internal memory you have, it's about how big your /data partition is. Apps can only install to this partition, and even if you had your internal memory empty, apps wouldn't be able to fill this memory because they are only stored in /data. To fix this, you can try to resize partitions, but it's not simple, so be sure to know what you're doing before you corrupt your partitions.