If for some reason you don't own a microSD card, you can still install the Oreo update via ADB:
1) Install ADB on your computer: https://www.xda-developers.com/insta...s-macos-linux/
2) Move update.zip to where your adb.exe file is
3) Enter the phone's stock Recovery and select "Apply Update from ADB"
4) Open a Windows Command prompt, go to where your adb.exe file is, and type "adb sideload update.zip"
Hope that helps! I was going crazy looking all over my house for a microSD card, until I realized it wasn't really needed