I will show you in that article how they set slots for admin respectively at the two hot stuffs
Keeping slots for AMX Mod X: you open addons\amxmodx\configs\amxx.cfg and search for
// Amount of reserved slots, amx_hideslots must be 1 to use this cvar (for more details see comments in plugin source)
amx_reservation 0
// If you set this to 1, you can hide slots on your server
amx_hideslots 0
How does must be preened those
amx_reservation 0 - here you can shoose how many position for admins you want
amx_hideslots 0 - Rather than you change to from 0 to 1 , they will not keep else slots