The only way you can have bigger boobs in one week is by having surgery! Even then I'm not sure if a week is long enough to recover - I don't know for sure. That's a bit drastic!
If you're asking how can you make your boobs 'grow bigger' in a week - then I'm sorry but it's impossible!
You can always wear a padded bra to make you look bigger. Or you could try standing tall and sticking out your chest and wearing tighter sweaters too!
Don't be self-conscious of your size - lot of beautiful girls have small breasts.