Go to the StreamingAssets\data\shipUpgrades folder and look for the argoUpgrade_podX.json files. Open them and look for the
{
"typeString" : "System.Int32",
"name" : "BarracksPods_Display",
"value" : 8,
"set" : true,
"valueConstant" : ""
}
The Value : 8 is the amount of mechwarriors you can have. Just be sure to edit the other files too, else your first upgrade might give you 50 members and the second will put it down to 16 again.