You can update an Asset package in the Package Manager window:
Open the Package Manager window.
From the package scope drop-down menu, select My Assets.
An arrow indicator appears next to any packages that have updates available.
In the list of packages, click the expander icon to the left of the Asset package’s name.
The newer version appears under the installed version.
Select the new version for the current package and see the details specific to that version in the details view.
Click the Update button.
When the progress bar finishes, the new package version information appears in the details view, and is immediately available.