to change the site on any g&g m4 series you have to knock the front pins out. under the sling mount is a little hex grub screw you have to take out then the front site will just slide off ( you will have to knock the pin out of the sling mount to get to the grub screw tho be careful )
you'd like that thing to be kind of cool like a bullpup, but you haven't figured out why exactly.
I suggest you get an airsoft tank.A bullpup airsoft tank. -jimski