How does one upgrade to Android SDK 25.1.3?

After the latest update to Xamarin, I get this error in design view

"The installed Android SDK is too old. Version 25.1.3 or newer is required."

Running the "Open Android SDK" and installing the latest version of Android Studio did not resolve the issue.

How do I update Android SDK?

Open the Preferences window by clicking File > Settings (on Mac, Android Studio > Preferences). In the left panel, click Appearance & Behavior > System Settings > Updates. Be sure that Automatically check for updates is checked, then select a channel from the drop-down list (see figure 1). Click Apply or OK.

How do I fix Android SDK is missing or corrupted?

Quick fix: Go to the Tools –> SDK manager –> SDK tools. Deselect Hide obsolete packages option on the right bottom and further install Android SDK Tools(obsolete). A new folder named Tools is now generated in the SDK directory.

I got past this by installing SDK v23 (Android 6.0). When designer mode finally opened, even though I also have Android 7.0 installed, Android 6.0 was the only selectable "Version" at the top of designer mode. I have Visual Studio 2015 btw.