can I upgrade from IOS 10.9.5 to Sierra?

Check to make sure your applications are compatible.

Application Compatibility

El Capitan 10.11 Compatibility information

macOS Sierra 10.12: Compatible Apps

Also check to make sure there is a compatible driver for your printer.

Do a backup before installing, preferable 2 backups on 2 different drives.

Yes, if your computer meets the minimum requirements How to download macOS Sierra - Apple Support