Will Not Install Gapps

I have just installed Blisspop rom and trying to install TKGapps. I have tried to install Full, mini and micro. I get not enough space to install and to run gapps-config.

How can I just clean out the /system/app folder so I can reinstall Bliss and then Gapps?

Is there a way to format the whole thing to remove everything, then reinstall Bliss (5.1.1) and gapps?

There is no way that I'm full up I have 12.28GB of space but it tells me that I don't. I'm getting really irritated.

Thanks in advance.