3.step: You have to minimum 4gb usb
4. step:Connect to switch with Putty or 2. Applacations
5.step:Power on switch
6-Press : space bar and after menu press Control+C Press 4 for Boot Menu.
Boot Menu 1. Boot [P]revious installed Junos packages 2. Boot Junos in [S]ingle user mode 3. Boot from [R]ecovery snapshot 4. Boot from [U]SB 5. Boot to [O]AM shell 6. Snapshot [B]oot menu 7. [M]ain menu Choice:Press 4 again for boot from USB.
6-step: installing new JUNOS (wait 10-15 minutes)
7.step : Completed
and you can login to switch for administration.
God luck 🙂