Do you need the space on your calendar?
Being new, can you hold out and build other accounts at a more worthy rate?
If so, then come first of the year announce that you have a price change. If they balk there is no shame in being honest...Tell them something along the line of..."When I started your windows I was new to the business and soon found I priced you too cheaply to be a viable business." They understand because they set their prices in order to stay in business too.
You don't want to race to the bottom of the scale. Hopefully you learn enough in the coming several months to confidently set your prices correctly for your needs.
Meanwhile, learn to be the baddest window cleaner on the Planet! Then charge as such.