Did you set your games to use the emulators you have installed ?
If you want to change your emulator for all your games in a platform you need to select your platform, then select all the games in the platform by pressing Control + A on the keyboard. Now with all the games selected press Control + E, this will start the bulk edit wizard. In the first dropdown menu select what you want to change which in this case is the emulator, then a 2nd dropdown menu will appear, select the emulator you want to change to. Now finish out the wizard and your games will be using the new emulator.
If you are getting a message saying you are running out of space then you probably have very little free drive space on one of your drives, possibly your C drive.