Login to your SlideME developer account and go to the application you wish to update. Click on "Edit" at the top of the page. Scroll down to your uploaded apk and click "Change". Replace the apk with the updated one. Then click "Save" at the bottom of the page.
Please note that if the updated apk has a new package name, application name, label or permissions, your application will go back to the approval queue.
If this apk is a new version of your application, make sure you have set a higher value on the versionCode, and check the box that reads "This is a new version of the application" before you click Save.