When loading, you will see an orange frame containing "Report Queued". This means that the data you are asking about is still loading. After a few seconds this will change to a green button with "Available" on it.
If "Available" is in a green frame, this report has not yet been downloaded.
If "Available" is in a grey frame, this report has already been downloaded.
Next to the report you would like to download is a blue "Download" button. If you click on this, the downloaded file will appear at the bottom of your screen for Google Chrome and at the top for Firefox. You can open it by clicking on it.
In Google Chrome:
Renew overview reports
If, after downloading certain reports, you want to see which ones are still to be downloaded, press the green "Renew" button. This button is located at the top right of the report list.