Most People Should Wait for the OTA
The Galaxy S8 Android Pie update is moving out slowly and it'll take months to complete.
If you don't want to wait for your Android update you can manually install the software right now if you have the right device, some patience, and some free time.
The official Galaxy S8 firmware is out which means some users can skip the OTA (Over-the-Air) roll out and manually install the software.
If you're feeling impatient, you might be tempted to go this route but you should only go through with it if you feel comfortable.
If you feel uncomfortable with any part of the manual installation process you'll want to hang back and wait for the OTA.
Manually installing the software can cause unforeseen issues (it's possible to brick your phone) so if you aren't feeling confident, hold off.