If you’re running low on storage it’s probably because you have apps that are taking up a lot of space with their cache. You also probably have apps installed that you no longer use. I have a 16GB iPhone so I’m frequently pushing the storage limits of my phone.
The first thing you’re going to want to do is uninstall apps that you are no longer using. If you later decide that you need the app you can always reinstall it.
Delete and reinstall apps where Documents and Storage is taking up a large amount of space. Here’s an example. Instapaper was taking up 496.3MB of storage on my iPhone. The app itself only uses just 50 MB of space. After deleting and reinstalling Instapaper it was using 67.3MB. Using this simple trick I was able to recovery 429MB of storage. That’s almost a half a gigabyte.
You can check to see how much storage every app on your phone is using by going to Settings > General > Storage & iCloud Usage > Manage Storage.
I ran across this third option the other day. I haven’t tried it so you’re on your own with this one.
Thorin Klosowski, Writing for Lifehacker
If you’re running low on storage, there’s a good chance its because you have some apps that are wasting a ton of space with their cache. In my case, I had several apps wasting about 1GB of space each, which is extremely problematic on a 16GB iPhone. When you attempt to download a large application, iOS will do anything it can to free up space for it, included clearing out the useless data in those apps and restoring them to their smaller sizes.
So, when you’re out of space, attempt to download a big app. The app has to be bigger than the amount of storage you have free. Hearthstone is a good one to try because it’s free and 1.89GB, but any large app will work. As you download it, head to Settings > General > Storage & iCloud Usage > Available. Here, you’ll see your storage space go up and down, and eventually the size of each application should start shrinking. Go ahead and cancel the Hearthstone download after the space is freed up or delete it when it’s finished downloading. Doing this, I went from 700MB available to 2.29GB.