Unfortunately there isn't anything you can do to make GD Library create better thumbs and samples. GD Library is a PHP module that is widely available on almost every server. PhotoStore uses GD Library to create the thumbs and samples for display. With out GD Library you would not have thumbs and samples at all. This does not affect the original image you uploaded, it is only the thumbs/samples that will look a little off compared to the original. There are other modules such as Imagemagick. Imagick will create a better thumb/sample than GD can, you can log into your manager -> settings -> software setup -> image processing and see if Imagick is available and turn it on/off if needed. If available on your hosting account you will be able to select it. If it isn't available it will be grayed out.
Ok I asked my hosting if they have Imagick installed and they said they do, but it is still grayed out?
That is because the hosting doesn't have imagick setup as a PECL extension in PHP. Once imagick is setup as a PECL extension in PHP then it will be available to turn on in the store manager.