Where is your work? Whether it is under Central Govt or State Govt. ?
If it is under Central Govt you need to apply for amendment for licence on plain paper by attaching original licence and pay additional security deposit @ 90/- per worker. No need to pay licence fee as you might have paid maximum licence fee of Rs. 375/-. No online facility is available in Central Labour department for renewal or amendment of licence.
If it is under State Govt, pl contact the office from where you have taken licence, they will tell you the required procedure because procedure and rate of SD is different from state to state.