From 'My Products' click 'Manage All' next to domains. Here you can check the appropriate domain(s) and then click the 'Renew' button.
from Manage All i can see all domains, domains that are about to expire it has renew now option
but the one i want to extend it doesn't have renew option
Try switching to Advanced View, looks like a bullet list with three dots followed by lines. There should be check boxes so you can select domains and a renew button in the toolbar.