Thank you everyone for those great tutorials. Unfortunately my Linux live usb stick wasn't working as expected.
So, after digging around. I found the solution to update it in Windows(or PE)
1. Make sure driver for the HBA is working correctly in Windows.
2. Download sg3_utils for Windows port.
3. Open CMD as administrator
4. Get device id of the SAS Expander from running >sg_scan -b -s ( You will get something like SCSI2:0,8,0 for the actual device ID)
You can also find current firmware version here.
5. Run >sg_write_buffer --mode=14 --in=dl-634a.rd2 SCSI2:0,8,0
6. After completion, run again above cmd with mode=15 and without the --in
7. Rescan with sg_scan, you should see the new firmware version.