iMovie won't update

I just upgraded my iMac yesterday to the El Capitan software and everything has renewed itself except for my iMovie which has stayed as the same version (9.0.9). I went to the app store to upgrade iMovie as it appears to have an upgrade, however everytime I press the upgrade button it does not display my apple id for me to put my password in and download it, instead there is a loading sign in the top left corner which will not go away.

I think it may have something to do with the downloading of El Capitan but I'm not too sure. Does anyone know how I can upgrade iMovie to version 10.1.1?