Don't Manually Install If You Aren't Comfortable
The Galaxy A's Oreo roll out is rolling out slowly. If you don't want to wait for the update to roll out Over-the-Air you can manually install the software right now.
If you're starting to feel impatient, you might be tempted to manually install the Android 8.0 Oreo update on your Galaxy A3, Galaxy A5, Galaxy A7, or Galaxy A8, right now.
Unfortunately, the process is more complicated than heading into settings to check for an update and it can be confusing for those that haven't sideloaded Android software in the past.
If you feel uncomfortable with any part of the manual installation process you should wait for your Galay A's Oreo update to arrive OTA.
If you aren't careful, you could wind up with a major headache.