The Fix for Cache not enough, please insert external SD card to download
1.First, you need a microSD card. A 2 GB capacity card will do just fine.
2.Next, when you insert a memory card into the Note 3, you are presented with the option to use it as internal memory or portable storage. Select portable storage.
3.Now, go run the software update again and it should download without popping up that error message any more.
If you got this error message on a smartphone other than the Infinix Note 3, the solution prescribed above should work too. Do give it a try.
Don’t forget to keep your phone well charged before running any software update. Also, be sure to back your files up to avoid losing any of them just in case something goes wrong during the update process.