"Apply Solution Upgrade" in Code or with WebApi

Hi,

I've been reading through the SDK 8.1 to find out how to:

1) Import a managed solution as Holding Solution
2) Apply Solution Upgrade

Purpose is to import my latest solution that include deletion of fields and hence get the fields removed from production environment.

I've managed to find answer for step number 1 by execution an ImportSolutionRequest:

ImportSolutionRequest impSolReq = new ImportSolutionRequest()
{
	CustomizationFile = fileBytes,
	PublishWorkflows = true,
	OverwriteUnmanagedCustomizations = false,
	HoldingSolution = true
};

This will import my solution as new holding solution. In the UI I can then press "Apply Solution Upgrade" to start the upgrade process.

I have not succeeded in finding the corresponding request for "Apply Solution Upgrade" in the SDK.

I'm running On-Premise CRM 2016 SP1 version 08.01.0000.0359

Hope someone have and can help me with an answer.

Kind regards,

Henrik