If you are still short on storage after uninstalling some unnecessary apps then you need to delete those downloaded files, for old pictures you can (Sync all of them with your computer or cloud service app's can help you out with this.
If you are noticing your phone being hanged try to restart it or let it rest for some time. However, if you are still facing the same issue then your phone may need an extreme factory reset. Go for it and save your phone.
Cut down on background tasks
Due to extreme usage of Smartphones these days we often forget to turn off background tasks however, paying a bit of attention can save your phone from any bigger issue. Hence, it is always handy to turn off Bluetooth or even WiFi when you are not using it.
Source: Cheat SheetÂ