What is the treatment for mild crowding a few years after braces due to teeth relapse? (Photo)

I had a severe case of crowding when I was 13 and I had braces for two years. After that I had fixed retainers on my lower teeth and I had a Hawley retainer for my upper teeth. I used it regularly the first year but afterwards I rarely used it. It has been two years and now my front teeth have shifted a bit, especially the front two teeth. There is slight crowding around the upper teeth as well. What are the treatments for this case and how long would it take to get it straight again?