If you haven't received an email yet, you can go to this link. Enter your e-mail address, click on 'Next' and then on 'Wachtwoord vergeten?'. You will now receive a password reset email after which you can log in.
Then go to the download page: https://www.sketchup.com/download/my-apps and download the SketchUp Pro 'Desktop Client'. The download page recognizes whether you are using Windows or Mac and offers the appropriate download for that.
For the full activation and installation process, see our manual or video: