Turn on iCloud Photos on your iPhone or iPad: Settings > [your name] > iCloud > Photos > Sync this iPhone
On Mac: System Settings > [your name] > iCloud > Photos > Sync this Mac
On Windows: install iCloud for Windows, sign in, and turn on Photos
Make sure you are signed in with the same Apple ID on all devices
Connect to Wi-Fi
Plug in your device if needed
Open the Photos app
Select the photos you want to move
Tap or click Share
Choose Save to Files or upload from the Photos app if available
If using iCloud Photos, keep the photos in the Photos app so they upload automatically
Wait for the upload to finish
Check iCloud.com > Photos to confirm the photos are there
Delete local copies only after confirming the photos are safely in iCloud