If you have sold an Investment, you can account for the sale in either one of two ways, depending on the Investment.

1) If it's a Position with automated price updates (equities, funds, ETFs, crypto, precious metals etc.) all you need to do is record a Sell transaction for the units you have sold. If you have sold all the units, the Position will remain in your Portfolio (or Wallet or Basket, depending on the Investment) in a dedicated section with value equal to zero, but the metrics on your Home page will include the performance realized on the Position.

2) If it's an Investment with manual input, you will find on the overview page of the Investment a "Close Holding" button, where you can record the date and the value of the sale. 
The Investment will no longer be visible on the left menu, but you can access it in the Holdings table on your Home page, in the "Closed Investments" section. The metrics on your Home page will include the performance realized on the Investment.