I´m trying to download the new ios7 update on my iPad but it tells me there is not enough storage, that I need 3.3 MG of storage. Well I bought more storage for $20 from the Apple Store and now I have 12.9 G of storage and I´m still getting the same message. What is the problem??
What you bought was iCloud storage - additional space in your iCloud account on Apple's servers.
Your device's storage cannot be upgraded - it is limited to whatever you originally bought - 16GB, 32GB or 64GB.
To free up space on your device, you will need to delete things on it. For example, transfer your photo's to your photo management software on your computer and then delete them from your camera roll. Or delete apps you do not need or use. Or delete music you have backed up on your computer and no longer listen to, or pdf's you have already read, or podcasts you've already listened to. But the only way to free space on your iPad is to remove some of what is currently taking up space on it.
You can also try plugging your iPad into your computer and use iTunes to update, as that will require far less space on your iPad since the download goes onto your computer and is run from there.