As Ivan says, if you are just updating the W kernel, no SMP, it isn't that hard to update, just need os2ldr and os2krnl. 104a is freely available.
Updating to SMP isn't that hard but as Lars impiied, to be stable, you really need the ACPI package from Arca Noae, which will update various components. The needed kernel etc are under x:\os2\install\smp.