Well, use a file explorer to find the app that you would like to remove. Alternatively, you can use ls to lis the files:
adb shell ls -1 /system/app/
Let's say you want to remove that game teeter. Before removing, you may want to make a backup:
adb shell cp /system/app/teeter.apk /sdcard/teeter.apk
Then:
adb shell rm /system/app/teeter.apk
If you have issues with file permissions, try downloading a terminal emulator app and doing the same thing and granting it superuser permissions.