Some ideas:

Get a copy of Burns, "Feeling Good Handbook" and work through the exercises.

Write out some positive affirmations about yourself and read them to yourself, looking in a mirror several times a day.

Write out some ideas of things you'd enjoy, and try to do one per day, like, go outside and look at the flowers...watch the birds at the birdfeeder...read a chapter in a new novel of an author you like, etc. Whatever you can think of that will give you a moment of enjoyment.

Hope this helps. The fact you WANT to change is important.