Something

		new upcmd[256], upindex;
	upcmd = strtok(cmdtext, upindex);

	if (strcmp(upcmd, "/up", true)==0)
	{
		new upnum;
		upnum = strval(strtok(cmdtext, upindex));

	    if(!strlen(upcmd)){
	    SendErrMsg(playerid, "Usage: /up <Amount to go up by>");
		return 1;
		}
  		new Float:x, Float:y, Float:z;
		GetPlayerPos(playerid, x, y, z);
		SendInfMsg(playerid, "You are moved up");
		SetPlayerPos(playerid, x, y, z + upnum);

		return 1;
  	}