Here is a link to the 3.2.1.3 firmware for the 62xx switch.  This would be the safest way to update.  www.dell.com/.../DriverDetails
We just purchased two 6248 switches and they came with firmware 3.1.1.0.  The latest version to update to is 3.3.3.3 and the firmware documentation states that there could be issues if you don't upgrade to 3.2.x first as it contains updates to the firmware management system.  "  Version  3.2  includes  improvements  to  the  firmware  management system.  You MUST follow the procedure set forth in the Dell PowerConnect 6200 Series Release 3.2 Upgrade Procedure included in the zip file to update the boot code AND firmware.  Failure to adhere to this procedure may result in your switch becoming inoperable. "  Is it safe to update to 3.3.x from 3.1.x ?  I don't see a download link on the support.dell.com site for the 3.2.x firmware.
Firmware Upgrade on 6248