To download the lattest firmware go to: https://software.cisco.com/download/navigator.html?mdfid=283009439&flowid=18904
From there find your model:
SG300-20 : https://software.cisco.com/download/release.html?mdfid=283019616&softwareid=282463181&release=1.4.7.06
Install new Firmware.
- Go to the upgrade page as shown in the picture and click Browse.
- Browse to the location were you're firmware file resides, select it and click open.
- Click APPLY to apply the firmware, it will take some time.
Then click on "DONE"
- When that's done, click on the ACTIVE IMAGE link.
- Select the latest IMAGE in "ACTIVE IMAGE AFTER REBOOT" and click APPLY.
- Then "CLICK" on the "REBOOT LINK"
- The reboot menu will appear, click on REBOOT"
Your switch will reboot and activate the latest firmware.
Note that the device might take some time for reboot.
After reboot check your configuration to make sure its all there.