DZABUZA

yesterday a repairman came and replaced our modem since the old one was malfunctioning(kept dropping connection and reseting) so now the connection is stable but now a new problem has popped up the bandwidth has been cut up by more than half im used to getting around 9Mbps where im now getting 3-4Mbps i called my isp and i did a test on my connection without the router and the result was 9Mbps. the isp said my router probably wasnt damaged but needs to be reconfigured anyone have any ideas why this has been happening? router model linksys BEFW11S4 .v4 thanks in advance~