As long they are both working as you want it to, then I see no reason to upgrade. Now there are many here who will disagree and say go to the latest and greatest. But if the device isn't broken, then there is no need to try to fix it.
As for the latest OS, check the sticky at the top of this section for the latest OS for your device and instructions. Remember, the OS is device specific so you will need one for the 8310, not 8300 or 8320.
The latest DM is 4.7 which seems to be pretty good, as is DM 4.5 and 4.6. But if you are using Windows 2000, Office XP, Office 2000 or an earlier version of Office, you will need to stick to DM 4.2 as the others are only compatible with Office 2003 and 2007 and XP/Vista.