This is for altering existing user access.
ga_users_update(
  linkId,
  update_object,
  accountId,
  webPropertyId = NULL,
  viewId = NULL
)The linkId to update
A list that will be turned into JSON that represents the new configuration for this linkId
Account Id
Web Property Id - set to NULL to operate on account level only
viewId - set to NULL to operate on webProperty level only
The new user object that has been altered.
Google help article on user permissions
Other User management functions: 
ga_users_add(),
ga_users_delete_linkid(),
ga_users_delete(),
ga_users_list()