VBA Userform Edit/Update record help

Dear Sir,

Please find the attached file of data entry userform.

you will find in sheet two buttons 1. Add data and 2 . Edit / Update data

My question is that ...
In edit/update data userform, when i click button update record then new rows create in excel it should not to be .
only update record which sr no i selected ..

can u help me in this vba coding .