Step 1:

  • Go to https://optifine.net/downloads
  • Click Download to the right of which Optifine you want depending on what version of Minecraft you want it for. E.g for 1.13.2 you want "OptiFine 1.13.2 HD U E5"
  • Wait a few seconds, then click SKIP AD in the top-right corner of the screen
  • Click the Download OptiFine link in the middle of the page.
  • Click Keep or Allow if your browser warns you that OptiFine might be dangerous.
  • Make sure you have already the version of Minecraft you wish to install Optifine with at least once.

Step 2:

  • Select Open with Java if it asks you what software you want to open it with.
  • Make sure the install path is C:\Users\owenb\AppData\Roaming\.minecraft
  • Click Install
  • A message should pop up saying it was successfully installed, click OK

Step 3:

  • Load the Minecraft launcher
  • The Optifine version of the game that you've just installed should be displayed under "play" in the green box at the bottom of the launcher.
  • If not then click on the up arrow on the left hand side of the "play" box and select the correct version.

Congrats! you've successfully installed Optifine for Minecraft!