Latest Software of iOS 7.0.3 Wont install ...
Do the Update using iTunes on the Computer you usually Sync and Backup to.
See the Using iTunes Section Here...
Make sure you have the Latest Version of iTunes (v11) Installed on your computer
- iTunes free download from www.itunes.com/download
... I don't want to buy more memory as I have already done.
Purchasing more iCloud Storage will Not Increase the Capacity of your Device. If it is a 16 GB Model it will ALWAYS be a 16 GB model.
What model iPad and what iOS version is it currently running?
If you have an iPad 1, the max iOS is 5.1.1. For newer iPads, the current iOS is 7.0.2. The Settings>General>Software Update only appears if you have iOS 5.0 or higher currently installed.
iOS 5: Updating your device to iOS 5 or Later
How to install iOS 6
iOS: How to update your iPhone, iPad, or iPod touch
If you are currently running an iOS lower than 5.0, connect the iPad to the computer, open iTunes. Then select the iPad under the Devices heading on the left, click on the Summary tab and then click on Check for Update.
Tip - If connected to your computer, you may need to disable your firewall and anitvirus software temporarily. Then download and install the iOS update. Be sure and backup your iPad before the iOS update. After you update an iPad (except iPad 1) to iOS 6.x, the next update can be installed via wifi (i.e., not connected to your computer).
Tip 2 - If you're updating via wifi, place your iPad close to your router to preclude getting a corrupted download.