[TadaoKumagai]

First,
If I were you, If I already have a Girlfriend and we are already in relationship for 4 year as you mention.

Then you have to ask yourself, What the Reason, Why you like her in the first place? What make you change, what make you distance from her? Is she the one who change, or are you the one who change?

Next, appearance of Girl number 2, which you know for 5 year. Ignore everything else, you feel attract to her because certain quality your 4 year GF lack, is found within Girl number 2.
I believe it the Quality or Characteristic that you like, not the Girl herself.

If that the case, just be completely honest, had a heart to heart conversation with your 4 year Girlfriend. Just communicate with her that you are not confident with the marriage as what you want is lack in her.

There a different between, cannot cook, don't want cook, refuse to cook, so which fall under her category? N, what household chore will you be contributing?
Don't expect you marry a Wife just to let her cook meal for you or clean the house, you can hire a maid for it (provided financial allow) , if not just make some agreement or arrangement. [If she in-charge of Cooking meal, then you in-charge Cleaning house]

Couple cover up each other flaws with each other strong point.

Whatever it is, you already propose to her, so just take responsibility of your own action.