B2 Visitor Visa extension

[tech2012]

Hi

My parents ( aged 62 years) have Visitor visa and they travelled 3-4 times to USA. Now Their B2 - Visitor visa is expiring in few months- Dec 2019. So How can I renewal their visa ?

Do they need to Go US consulate office for stamping again ? or Do they eligible for IWP / Dropbox option ?


Please guide me the process.



Thanks