Free Cloud services provide limited storage, and you should be careful about storage left. On Galaxy S4 you have limited storage via your Samsung Account and you can always check storage usage by following the instructions:
1. Open "Settings" and choose "Accounts" tab
2. Tap "Samsung Account"
3. Tap "Storage Usage"
4. The system starts to calculate your storage usage in different categoires (Memo, S Planner, Internet, Contacts, Backed UP data)
Read More Galaxy S4 Tips and Tricks