Sir, in your case both Share transfer and sale imply the same meaning. Generally shares of private limited companies are transfered through private placements on payment on stamp duty and execution of share transfer form (as shares are unlisted this is the only means).
The form has to be submitted to the company which on verification will transfer the same to the transferee and make necessary changes in the Member's register. Complete the entire process within 60 days with all procedures properly followed(time frame and procesures u/s 56 of Companies Act 2013).
On completion of this you are releived of all your liablities for the shares held, except in case of partly paid up shares and the company is wound up within a year of transfer. Otherwise your clear.