You may not enough available storage space. So suggest you free up some space.
The GB size of the download file is the compressed size (like .zip or .dmg). When the file is installed/uncompressed it can be 2-3 times larger.
How much space is used by your Other? You may be able to reduce.
How Do I Get Rid Of The “Other” Data Stored On My iPad Or iPhone?
http://tinyurl.com/85w6xwn
How to Remove “Other” Data from iPhone, iPad and iPod Touch
http://www.igeeksblog.com/how-to-remove-other-data-from-iphone/
With an iOS device, the “Other” space in iTunes is used to store things like documents, settings, caches, and a few other important items. If you sync lots of documents to apps like GoodReader, DropCopy, or anything else that reads external files, your storage use can skyrocket. With iOS 5/6/7, you can see exactly which applications are taking up the most space. Just head to Settings > General > Usage, and tap the button labeled Show All Apps. The storage section will show you the app and how much storage space it is taking up. Tap on the app name to get a description of the additional storage space being used by the app’s documents and data. You can remove the storage-hogging application and all of its data directly from this screen, or manually remove the data by opening the app. Some applications, especially those designed by Apple, will allow you to remove stored data by swiping from left to right on the item to reveal a Delete button.
What is “Other” and What Can I Do About It?
https://discussions.apple.com/docs/DOC-5142
iPhone or iPad Ran Out of Storage Space? Here’s How to Make Space Available Quickly
http://osxdaily.com/2012/06/02/iphone-ipad-ran-out-of-available-storage-space-ho w-to-fix-quick/
6 Tips to Free Up Tons of Storage Space on iPad, iPhone, and iPod Touch
http://osxdaily.com/2012/04/24/6-tips-free-up-storage-space-ipad-iphone-ipod-tou ch/
Also,
How to Clear Message/iMessage Cache on iPhone & iPad And Reclaim Lots of Free Space
http://www.igeeksblog.com/how-to-clear-message-imessage-cache-on-iphone-ipad/
When did you buy your iPad? If after 1 Sept 2013, you can download those apps for free.
How to get all the iWork apps, iPhoto, and iMovie for free on an eligible iPhone or iPad
http://www.imore.com/how-get-all-iwork-apps-iphoto-and-imovie-free-eligible-ipho ne-or-ipad
About Free Apple Apps for iOS 7 compatible devices
http://support.apple.com/kb/HT5913
Cheers, Tom 😉