Self-Esteem I find is highly related to willpower. Whatever is the root of your tendancy to have low self-esteem, you can decide to turn it around in a few steps:
1 - define a challenge you want to take up. Not to easy, not too difficult. Something you would be very proud to have accomplished (ex. losing 5 kg in 2 months, running a marathon, changing job, start a new sport activity, join a club, be promoted...).
2 - Now, you have to understand that if you want it, you can get it. It is all about willpower. Declare it to a few friends, ask for their support to help you achieve this goal, and be serious about it. Prove yourself that you are in control, and what you want in life, you can get it. Basically, "nothing is impossible for a willing heart".
3 - Once you have achieved this goal (friends' support is key, but you can use many motivational tools, platforms etc... also to help), you will feel very proud, and the success will only be thanks to you, wanting something and working to get it. No excuses, just you.
After that, you should feel very proud and feel you are capable of everything. People will admire you, and you will regain confidence and self esteem I am sure (+ build a real life story that is yours).
Hope this will help.