How to upgrade to latest WDA and XCUITestDriver without uninstalling Appium?

Can some one please tell me how can I upgrade the WebAgentDriver and XCUITestDriver in v1.6.4-beta without uninstalling Appium? I see that XCUITestDriver keeps updating its versions often but Appium would pick up the latest version only when we re-install Appium.

If it is not possible, can you please tell me how should I upgrade WDA?

Thanks in advance.