How can I check/upgrade Proguard version when using it in Eclipse for Android development?

The ProGuard jar is located inside the Android SDK: android-sdk/tools/proguard/lib/proguard.jar

You can print out its version number with

java -jar android-sdk/tools/proguard/lib/proguard.jar

(with the proper path). If necessary, you can replace the jar (actually, the entire proguard subdirectory) with the latest version from the download page at the official ProGuard site.

For the visually inclined, the version of Proguard can also be checked by double clicking on proguardgui.jar in ...\android-sdk\tools\proguard\lib