Can't access multisite dashboard after update to 4.2

Hello, I updated my multisite network (iowapga.com) to WP 4.2 I went through all of the steps and also updated network database, etc. Now, when I try to go into another dashboard besides my main dashboard, it tries to load but nothing happens. It just spins. I have two subdomains setup and it does the same thing for each one.

Assuming that this may have something to do with an incompatible plugin on the subdomain. Was wondering how I go about deactivating plugins when I can't get to dashboard. I know how to get into ftp and do the trick of renaming plugin to deactivate it but wasn't sure if there is a special folder where I need to do that or the general wp-content/plugins folder.

Any help would be greatly appreciated. Thank you.