Applications can take up a large amount of storage on devices. To create more storage on your Galaxy Ace you can purchase a Micro SD card. This slots in to the device and allows applications and data to be saved externally. Please visit the link below which shows you the different types of Micro SD cards that are available.
If you do not wish to purchase external storage you can try deleting data from your device. Deleting items such as pictures, emails, and text messages can all create more storage on the device. You can also try clearing your internet history and cache. Please follow the steps below on how to clear the cache individually.
Settings > Application Manager > Select Application > Clear Cache
You can also check which element of the device is taking up the most storage. You can do this by going to Settings > Storage. This will allow you to view all the storage on the device and manage it accordingly. You are also able to clear all cached data from every application you have rather than going through them individually. Once you have acknowledged what is taking up the most storage on your device you can get a better understanding of what needs to be removed.
I hope this helps.
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