This isn't everyone's method, but what I tend to do is I have two wordpad folders open - one with the original application and one with a blank version. I then basically start the application over again, copying it from the first file and rewriting it, and as I go I mentally edit out the bits that I believe don't fit with the character. This really helps me, but I understand that not everyone can do that. I do suggest going through a blank application and basically writing out what you want in each section.
For example, personality you could go "PERSONALITY - prone to fits of anger, kind-hearted, doesn't like to be pushed around but is a sucker for her friends, has her fair share of bad habits (such as)..." and with history, you can write out the events that you definitely want to include. Like "HISTORY - born to ______ and ______. Grew up in _______. At age of 3, ______ happens. She goes to school at _______. In her _____ year, _____ happened. She gained her powers at the age of _________, and struggled with her ability to control them. Example here of something going wrong or how she discovered it. Difficulties she faced. Family problems. Friends." When you do this, you should be able to start seperating them and building them into paragraphs. Writing an application, even a rewrite, is basically just a lot of characteristics and facts thrown together in a coherent format.
Also, one thing I would suggest is getting someone you know that will be honest with you - if you feel that something in your rewrite sounds off, or unrealistic, then it probably is. It's always good to have someone who will be blunt with you because that makes for better applications in the end. For example, chaperoned is who I go to with those sorts of things as she'll tell me if something sounds ridiculous. Also, don't be afraid to let the character go in a different direction if you suddenly start coming up with one. I can't tell you how many characters I pictured as one way and they turned out completely different.