if it is a public company or a subsidiary of a public company the shares can be sold off at any point of time after the issue. The primary concept of the companies act is to let the individuals have freedom to sell/purchase shares traded at a stock exchange. You can sell the same at open market or convert them into equity shares at your behest
I don't think it is a good idea to sell preference shares as they gove you benefits over equity shares, these are good for investment and even if a company plans to go into liquidation preferrential shareholders will be the first to get their money back, so they are definately better than equity shares.
