If you want to sell your stock positions, then you must send a sell order to your broker-dealer.
To do this, most broker-dealers have the option of selling directly on their platform. All you need to do is log on to your account, click into your share position and choose the amount you want to sell.
Please be aware that some broker-dealers have a settlement period before you can withdraw, or reinvest those funds. Please check your brokers policy on this.