Hi REGIT, I strongly suggest you to upgrade their old software release (WB.15.11.0007 which uses BootROM WB.15.04, March 2013) with latest available of WB.16.09 software branch (WB.16.09.0003 which uses BootROM WB.16.03) or, if you like a more conservative approach go to latest available of WB.16.02 software branch (WB.16.02.0027 which, as it happens for WB.16.09.0003, uses BootROM WB.16.03 too)...and do so using CLI via SSH, Telnet or Serial Console...forget about using Web Interface...CLI is truly better and faster. You have to consider that if your switch has an older version of BootROM, the BootROM will be automatically updated first (so the switch will reboot twice) with this version of software you're providing.
If you need help with commands/procedures just tell us.