get into the shiparch.ini and do the following (using the patriot as an example)


[Ship
ids_name = 237034
ids_info = 66570
ids_info1 = 66571
ids_info2 = 66608
ids_info3 = 66572
ship_class = 0
nickname = li_fighter
LODranges = 0, 40, 60, 140, 300, 1000
msg_id_prefix = gcs_refer_shiparch_Liblf
mission_property = can_use_berths
type = FIGHTER
mass = 100.000000
hold_size = 25 <----change this number to 200 and your cargo size is now 200
linear_drag = 1.000000
fuse = li_fighter_gas01, 0.000000, -1
fuse = li_fighter_smoke01, 0.000000, -1
fuse = intermed_damage_smallship02, 0.000000, 400
fuse = intermed_damage_smallship03, 0.000000, 200
max_bank_angle = 35
camera_offset = 6, 22
camera_angular_acceleration = 0.050000
camera_horizontal_turn_angle = 23
camera_vertical_turn_up_angle = 5
camera_vertical_turn_down_angle = 30
camera_turn_look_ahead_slerp_amount = 1.000000
nanobot_limit = 12
shield_battery_limit = 12
hit_pts = 1300

the hold size relates to the cargo capasity of ships