Decided to write a tutorial for those who are voting this year. This tutorial is translated from what the Chinese fans wrote up, so take away what you can.
Before voting
Change to a Japan I.P address on your mobile phone, if you want to be 100% sure your vote goes through.
To do that, download a VPN app from Appstore/Playstore and do necessary settings to change your I.P address. You can double-check your I.P address here.
(C-fans advise against using your computer as this may result in the vote not going through.)
Begin Voting
Step 1: Access the voting URL. You will see 2 boxes, just click on the right side which I highlighted in Red. This side allows you to search by Team.
Step 2: Now scroll down and search for the Team of the member you wish to vote for. Pls note, Nyan Nyan Kamen aka Kojima Haruna is still in AKB48, but in a league of her own!
Step 3: All the members’ names will be listed in Kanji. If you are still unsure about the Kanji of the member you’re voting for, click in so you can see their photos.
Step 4: This photo page is where you enter your SERIAL CODE. Scroll to bottom.
Step 5: Enter the serial code into the 2 boxes. Click on pink button at the bottom 投票。
END: A message indicating that your vote has been submitted appears. With timestamp.
If you have other codes to enter, click on the grey button to start again.
AKB48’s new single comes with voting ticket for upcoming elections. Purchase their single below:
AllThingsJpop 
How to get a serial code?
You need to buy the CD.