How do I release an update for my app? I can not find an update apk option on the developer console.
You just upload a new apk file, which should have a higher version code and a higher version number than the previous apk.
As Pompe says; but also be aware:
Before uploading the updated application, be sure that you have incremented the
android:versionNameattributes in the element of the manifest file. Also, the package name must be the same as the existing version and the .apk file must be signed with the same private key. If the package name and signing certificate do not match those of the existing version, Market will consider it a new application, publish it as such, and will not offer it to existing users as an update.
Remember that you always have use the same key that you used to sign the first release version. If you sign a new version with a different key, you will get an error message when trying to upload it.
As said in other replies, make sure that you have increased the versionCode and versionName in the manifest.xml