You can choose to automatically update Remix OS:
Go to 'Settings' > 'Upgrade' > 'More' > 'Upgrade settings' > Select 'Automatically install updates'
Please make sure you are connected to Ethernet or Wi-Fi. The OTA updater will only automatically download and update if you are connected to the Internet.
OR manually update Remix OS:
Go to 'Settings' > 'Update'. Then download and install the update.