You would need to open a ticket (as Hashbrowns said), though be advised: once this is done, blizzard support is unlikely to undo this if you change your mind.
Plus, blizzard support is more likely to link (and thus consolidate) accounts than otherwise to counteract account trades, so it maybe trickier to unlink accounts than to link accounts. Still, cases of support unlinking accounts do exist, so opening a ticket is worth a try.
Also, the DK-on-F2P-account bug on moon guard is still active, if you plan to start anew instead.