I need to upload a simple beam model from Revit then to update it's height or width from a web app endpoint
Is this possible?
Yes. You can perform such a manipulation in a live local session of Revit.exe on your Windows system using the .NET Revit API. Providing access to that same functionality in the cloud with no local installation of Revit is one the main purpose of the APS Design Automation API. Check out the documentation, code samples and blog posts there for more details.