A new firmware has been released for the following recorders:
DVR-1590, 1600, 4480, 4575, 4780, 4980, and NVR-7450 & 8580

Here are the new feature highlights:

• Updated P2P SDK library to improve connectivity and overcome more complex networks
• Changed e-mail sender name from using email address instead of DVR/NVR name
• Update the UI to be common on all DVRs and NVRs
• Updated the workflow for password recovery via email or entering MAC address directly
• NVRs now copy the NVR password to the IP camera and use it automatically
• Restart the P2P library every 24 hours to ensure any IP address changes are captured
• Updated the method of Dropbox authorization to use the new OAuth2 system and general improvements to Dropbox setup
• Add support for PIR IP cams to all NVR8-7450
• Add support for PIR 1080MSB/MSD to DVRx-1590 and 1600 with Push notifications
• Added full support to DVRx-4575 for PIR cams, Push and Dropbox
• Improved PIR detection for PIR cameras.

You can download the firmware from the links below; be sure to choose the right model based on your Device Type when you access Menu > System > Info.

• 4 channels
  • DVR4-1590
  • DVR4-1600
  • DVR4-4480
  • DVR4-4575
  • DVR4-4780
  • DVR4-4980
  • NVR4-7450
• 8 channels
  • DVR8-1590
  • DVR8-1600
  • DVR8-4480
  • DVR8-4480V/DVR8-4580V
  • DVR8-4575
  • DVR8-4780
  • DVR8-4980
  • NVR8-7450
  • NVR8-8580
• 16 channels
  • DVR16-1590
  • DVR16-1600
  • DVR16-4575
  • DVR16-4780
  • NVR16-8580

You can then proceed to this article for steps on how to update your recorder:
How to manually update my recorder?