On Android 7.1 Nougat you can find the ‘Manage storage’ option under Settings > Storage, where you’ll be able to clear storage space from your device.
Within Settings > Storage you’ll find a breakdown of the storage on your Android 7.1 device. With previous Android versions you would only be able to see storage usage per category, but in v7.1 you’ll see a ‘Manage storage’ option right at the top.
If you tap on the option, you’ll be presented with two options – the automatic ‘Smart Storage’ and the manual option to ‘Free up space now’.
Within the settings you’ll also get a more detailed breakdown of the apps taking up storage space – you can see this by tapping on one of the options, such as ‘Apps’ and seeing the apps which are taking up the most space on your device.
The automatic option:
The ‘Smart Storage’ option will automatically remove backed up photos and videos when you’re almost at full capacity on your Android device. Your device won’t delete non-backed up photos or videos, so you don’t have to worry about losing important memories as they’ll be backed up to Google Photos.
If you have a Google Pixel, then you’ll get free storage of photos and videos at full resolution.
The option you’ll see to ‘Remove backed up photos & videos’ will allow you to select the number of days old the photos and videos have to be, before being considered for automatic deletion.
The manual option:
The option to ‘Free up space now’ gives you the ability to clear your storage right away. You have the option to clear your downloads folder straight away, even photos & videos and apps that are older than X amount of days… source