If an audio file is too loud, if a photo does not fit or a background image would fit better to the text if it were mirrored, you will have to edit the files before you upload them. Here are some free online tools you can use:
Browser-based tools
for editing photos and audio files (without download):
Free online photo editing:
This free tool helps you to edit pictures directly with options like changing the size, cropping, mirroring or adding effects.
Free online audio editing
Free software for downloading:
Free audio editing software
Audacity for Windows
http://www.chip.de/downloads/Audacity_13010690.html
Audacity for Mac
http://www.chip.de/downloads/Audacity-fuer-Mac-OS_31901383.html
Free photo editing software
Gimp for Windows
http://www.chip.de/downloads/GIMP_12992070.html
Gimp for Mac
http://www.chip.de/downloads/Gimp-fuer-Mac-OS_22783981.html
Direct link
http://gimp.lisanet.de/Website/Download.html
Free video editing software
MovieMaker for Windows
http://www.chip.de/downloads/Windows-Movie-Maker_13007023.html
Blackmagic Fusion for Windows
http://www.chip.de/downloads/Blackmagic-Fusion_73983556.html
Shotcut for Mac
http://www.computerbild.de/download/Shotcut-Mac-8909172.html