Once logged in to your account, navigate to "Holdings" -> "Loans". Use the filter to only show the investments you want to sell and mark these using the checkboxes. Click "Sell selected investments" on the screen and follow the instructions.
Keep in mind that sales on the secondary market include a 5% fee and that your investments are not sold directly; it may take a day or two for your investment to be bought by other investors.
Depending on your bonus level, the fee may be less, up to 2%. Read more here Bonus system.
For the Balanced strategy, you also have the right to sell investments free of charge up to a total of SEK 50,000 after each twelve-month period.