Version 2.0.0 introduced breaking change in library API in order to fix breaking change introduced by Forge API itself.
The withMemoryOf method of \Laravel\Forge\Servers\Providers\Provider has been removed because Forge changed the way
it handles server sizes across all providers & their regions.
Now you should refer to /api/v1/regions endpoint to list all available regions & server sizes that are available
in regions. Also @acurrieclark made list of provider regions
and server sizes but those lists may become outdated in future.
Now when you have your size identifier, use the withSizeId method to specify your new server's size:
<?php
use Laravel\Forge\ApiProvider;
use Laravel\Forge\Forge;
$forge = new Forge(new ApiProvider('api-token'));
$credential = $forge->credentialFor('ocean2');
// The "1" size ID is 1GB droplet with 1 CPU.
$server = $forge->create()->droplet()->withSizeId(1);