Visas on arrival (100 QR) can be renewed once (for an additional 100QR) then you have to leave the country and return (Bahrain Air has fares in the range of 411 QR).

 

I'm not sure if a tourist visa obtained through a hotel can be renewed though. You can try renewing it at the Immigration Office near the airport. If you do, great, if not, Bahrain has a great First Class lounge--far surpassing the public bus terminal called the Silver Lounge at DIA.