Hello and welcome to the support community
The highest version of flash available for Mac OS X 10.3 is version 9.0
Yes you can upgrade the OS depending on which version of the iBook you own and how much memory you have installed. If your iBook processor speed is above 800mhz then you could install Mac OS X 10.5.8 Lepoard.
If your iBook is 800 MHz then you could upgrade to Mac OS X 10.4.11 Tiger
Hope this helps.
Which version of the Mac OS your iBook can use depends upon which model it is, the available space on the hard drive (as well as the total capacity of the hard drive), how much RAM is installed, and whether it has the capability to read DVDs.
Mac OS X 10.4 (Tiger) System Requirements:
Mac OS X 10.5 (Leopard) System Requirements:
As you have found out, which version of Flash you can use depends upon which version of Mac OS is installed.