function main(projectId, zone, instanceName, newMemory) {
  // [START compute_custom_machine_type_update_memory]
  /**
   * TODO(developer): Uncomment and replace these variables before running the sample.
   */
  // const projectId = 'YOUR_PROJECT_ID';
  // const zone = 'europe-central2-b';
  // const instanceName = 'YOUR_INSTANCE_NAME';
  // const newMemory = 256;

  const compute = require('@google-cloud/compute');

  async function modifyInstanceWithExtendedMemory() {
    const instancesClient = new compute.InstancesClient();

    const [instance] = await instancesClient.get({
      project: projectId,
      zone,
      instance: instanceName,
    });

    if (
      !['machineTypes/n1-', 'machineTypes/n2-', 'machineTypes/n2d-'].some(
        type => instance.machineType.includes(type)
      )
    ) {
      throw new Error('extra memory is available only for N1, N2 and N2D CPUs');
    }

    // Make sure that the machine is turned off
    if (!['TERMINATED', 'STOPPED'].some(status => instance.status === status)) {
      const [response] = await instancesClient.stop({
        project: projectId,
        zone,
        instance: instanceName,
      });

      let operation = response.latestResponse;
      const operationsClient = new compute.ZoneOperationsClient();

      // Wait for the stop operation to complete.
      while (operation.status !== 'DONE') {
        [operation] = await operationsClient.wait({
          operation: operation.name,
          project: projectId,
          zone: operation.zone.split('/').pop(),
        });
      }
    }

    // Modify the machine definition, remember that extended memory
    // is available only for N1, N2 and N2D CPUs

    const start = instance.machineType.substring(
      0,
      instance.machineType.lastIndexOf('-')
    );

    const [response] = await instancesClient.setMachineType({
      project: projectId,
      zone,
      instance: instanceName,
      instancesSetMachineTypeRequestResource: {
        machineType: `${start}-${newMemory}-ext`,
      },
    });
    let operation = response.latestResponse;
    const operationsClient = new compute.ZoneOperationsClient();

    // Wait for the update operation to complete.
    while (operation.status !== 'DONE') {
      [operation] = await operationsClient.wait({
        operation: operation.name,
        project: projectId,
        zone: operation.zone.split('/').pop(),
      });
    }

    console.log('Instance updated.');
  }

  modifyInstanceWithExtendedMemory();
  // [END compute_custom_machine_type_update_memory]
}
Sends an update instance machine type request to the Compute Engine API and waits for it to complete.

@param {string} projectId - ID or number of the project you want to use.
@param {string} zone - Name of the zone you want to use, for example: us-west3-b
@param {string} instanceName - Name of the new machine.
@param {int} newMemory - The new amount of memory for the VM instance, in megabytes.