Hi,
First check your onboard memory to see what is using it up.
The phone does have a limited amount of internal storage capacity.
Look at clearing your browser history and caches.
Go into settings > Applications and clear data &cache from your most used apps. Facebook is the usual culprit that uses a lot of storage space.
Clear ;
e mails and attachments.
sms and mms messages.
Tones and games you no longer use and their accumulated data.
Apps you rarely use.
Videos.
If their seems to be ample then perform a soft reset as it may just be a glitch.
To soft reset your phone press and hold the Power/Lock button for a 2-3 seconds and the phone will restart.
Wait about 10 seconds and then press and hold the Power/Lock button again to restart. If that doesn't work, then remove the battery (if it has one).
Wait 30 seconds and put the battery back in.
Then press the Power/Lock button to turn the phone on.
I don't believe you will need to carry this out.
Occasionally a hard reset can help phone issues, but make a back up first as this typically deletes saved data. This is to be carried out as a last resort.
http://www.hard-reset.com/samsung-galaxy-ace-2-i8160-hard-reset.html
Ensure your on the latest firmware.
