You can stop feeling like a loser by changing how you think and act. However, "loser" is a subjective term, meaning that there is no way to stop or start being a loser.
Many people who feel like losers may feel that way because some cultures place unrealistic expectations on people. If you do not make a certain amount of money, if you do not look a certain way, if you do not possess certain talents, you may feel that you are not worth as much as some other people.
One way to get around this is to change how you think about yourself. Rather than focusing on your negative traits, think of things that make you a good person. Think about the last time you made somebody happy or did the right thing even when it was hard.
Sometimes, you may feel like a loser because you made a mistake or did something bad. If this is true, you should figure out how to best correct your mistake, make amends to the people you may have harmed, and set a goal not to make that mistake again.
Finally, some basic lifestyle changes can help you feel like a winner. Exercise, connect with others, and focus on the positive.