1. To directly view Sales and Trends from iTunes Connect Site:
1.1. Go to iTunes Connect: http://itunesconnect.apple.com
1.2. Log in with your credentials
1.3. Click on Sales and Trends
1.4. Here you can see the iOS downloads by Daily, Weekly, etc.
2. To reach from Apple Developer Portal:
2.1. In Member Center sign in to Apple Developer Portal: http://developer.apple.com
2.2. Click iTunes Connect under Developer Program Resources
2.3. Sign into iTunes Connect with correct login credentials
2.4. Click Sales and Trends in iTunes Connect window
2.5. Here you can see the iOS downloads by Daily, Weekly, etc.