How do I remove/delete an app from my iPad mini that I no longer need?

Press and hold any of the apps and after a couple of seconds or so they should start to shake. Then press the 'x' in the top left corner to delete the ones that you don't want, and when you've finished deleting press the home button so as to stop the shaking. If you don't get the 'x' on any of the apps that you've downloaded (you can't delete built-in apps) then check that Settings > General > Restrictions > Deleting Apps isn't set 'off'

i I need to enter the passcode when I go to restriction, but I forgot the passcode, how can I retrieve it?

You can't retrieve it. You have to restore your iPad as new in order to remove the restrictions passcode.

If you lose or forget your Restrictions passcode, you'll need to erase your device and then set it up as a new device to remove the passcode. Restoring the device won't remove the passcode.

About Restrictions (parental controls) on iPhone, iPad, and iPod touch - Apple Support