unable to upgrade firmware

Hi, we just purchased these Dell X series PowerConnect switches and we decided to upgrade the firmware ASAP since the GUI is really slow and we're not sure if upgrading the firmware can help. Our existing firmware is:

Firmware: 3.0.0.80

Boot version: 1.0.0.17

HW Version: 00.00.02

Ok here's my issue. I went to 

https://support.dell.com/ 

and download the latest firmware of this switch. I had a file named:

sw_tz-100__eng_5.9.1.7.sig

I went to the GUI under Switch Management > File Update and Backup and click on Edit

IP Format: I just left it at IPv4

none for IPv6

File Type: Firmware Download

Update method: At first I selected USB since that's the easiest but whenever I clicked on OK, it just shows me 

Error encountered in copy operation: Driver is not connected

So I selected TFTP, I used OpenTFTPServer downloaded thru SourceForge.net

same error message as well. Am I lacking something here? 

Thanks

Jeff