Trade in or Part-Exchange. The easiest but most expensive route. Dealer takes all. You pay his full price and he gives you 'bottom book'
Sell privately. Fraught from the start. Stay in all hours to meet wheel kickers and test pilots. Your car must be up to scratch and fully valeted to stand any chance. Presentation is key
Auctions / Car buying websites. A lot of leg work for little gain after entry fees/commission/VAT are deducted assuming a bid is made at all.