Well depends on your registration system make the following code suitable to it.
pawn Код:
CMD:makeadmin(playerid, params[])
{
if(PlayerInfo[ playerid ][ PLAYER_LEVEL] < 5) return SendClientMessage(playerid, -1, "ERROR: You are not high enough level bla bla");//If his level is less than 5 he can't use this command
//Change the line above to be suiable
new level, aname[MAX_PLAYER_NAME];//Variables to be used further on
new targetid;//This variable will be assigned to the dude who's level will be changed
if(sscanf(params, "ui", targetid, level)) return SendClientMessage(playerid, -1, "ERROR: /makeadmin (playerid/name) (level)");
if (level > 5 || level < 0) return SendClientMessage(playerid, -1, "ERROR:INVALID level");//This will limit the levels from 1 to 5,(editable)
if(!IsPlayerConnected( targetid )) return SendClientMessage(playerid, -1, "ERROR:INVALID player");//This will be called incase the player isn't connected
new string1[130], tname[MAX_PLAYER_NAME], string2[130];//String to send
PlayerInfo[targetid][ PLAYER_LEVEL ] = level;//This part will set his level
GetPlayerName(playerid, aname, sizeof(aname));
GetPlayerName(targetid, tname, sizeof(tname));
format(string2, sizeof(string1), "Admin %s has set %s's level to %i", aname, tname, level);//This will be sent to all players
SendClientMessageToAll(Yellow, string2);
return 1;
}