You know when a chalkboard or whiteboard is erased, but the residue from the writing is still there? If you just choose to write over the smudges, what you're writing is difficult to read. And if you just keep erasing and trying to write over it, the board only gets dirtier and dirtier. It's in those times you need a cleaning solution, or back in my day water, to truly get the board clean.
The same concept applies to our thinking. If we try to 'erase' negative thoughts and patterns on our own, it only muddies things up. We try so hard to change things, but it only seems like our efforts make things worse.
It's only by using the Word of God will we truly bring change to our thinking. In Ephesians, Paul talks about how Christ cleanses the church by the washing of water by the Word so the church can stand before Him holy and without blemish. (Ephesians 5:26, 27)
One thing you can bank on is the truth of God's word. His word will stand no matter what else is going on. He is not like man and will never lie to you. What He said in His word is true, and his thoughts toward you are to bring you to a good conclusion. (Jeremiah 29:11)
You really want to start fresh? Take some time and get some scriptures that speak to you in your situation. Read those scriptures, memorize them, repeat them to yourself, and let God's Word get down in your spirit! Allow those words from God to wash away the negativity and all the other adverse opinions that are clouding your thinking and holding you back from moving forward.
Don't let the past muddy up your thinking. Start fresh!