Thanks for posting in the Apple Support Communities Jennakoenig,
If you use iCloud, the following steps will allow you to download the full size video from the cloud:
1: On iCloud.com, click Photos and select a photo or video. Hold the command key on your Mac or control key on your PC to select multiple photos or videos.
2: Click and hold the download button 
in the upper corner of the window. If you want to download your photo or video as it was originally captured or imported, choose Unmodified Original. For JPEG or H.264 format — including edits, and even if it was originally in HEIF or HEVC format — choose Most Compatible.*
3: Click Download.
If your photos download as a ZIP archive, learn how to uncompress the folder on your Mac or your PC.
You can also download the videos from within the app, using these steps:
1: Open the Photos app.
2: Choose Photos > Preferences.
3: Select iCloud, then click Download Originals to this Mac.
You can find these steps and additional information you may find helpful, here: Download iCloud photos and videos
Alternatively, you can import photos and videos to your Mac using a USB cable, by doing the following:
1: Connect your iPhone, iPad, or iPod touch to your Mac with a USB cable.
2: Open the Photos app on your computer.
3: The Photos app shows an Import screen with all the photos and videos that are on your connected device. If the Import screen doesn't automatically appear, click the device's name in the Photos sidebar.
4: If asked, unlock your iOS or iPadOS device using your passcode. If you see a prompt on your iOS or iPadOS device asking you to Trust This Computer, tap Trust to continue.
5: Choose where you want to import your photos. Next to "Import to," you can choose an existing album or create a new one.
6: Select the photos you want to import and click Import Selected, or click Import All New Photos.
7: Wait for the process to finish, then disconnect your device from your Mac.
You can find these steps, here: Transfer photos and videos from your iPhone, iPad, or iPod touch to your Mac or PC
We hope this helps!
