We need more info. Do you want to upgrade the hardware or the software? Also, I am not familiar with "eMac 9.0" as one of the four eMac variants. The best way to find out exactly which eMac variant you (the variant affects your upggrade option) please refer to this Apple article:
and follow those instructions to find your serial number and, from that, your variant.
NOTE: Please DO NOT post your serial number in these forums. just the model name you find for your eMac.
With that, we can better advise on upgrading.