Manual: Picasa - resize your images
Open Picasa and select the folder that contains the pictures to be resized.

Select the picture (or group of pictures) that you are going to resize and add to the website. The pictures you selected should also be shown in the picture tray at the bottom left corner of the screen.

Click on the File menu and then click on "Export Picture to Folder..."

In the Export to Folder Window, adjust the settings as follows:
a: Location of exported folder. Click on "Browse..." and select your website's folder. If your website has a folder for images, you should select such folder instead.
b:Name of exported folder. Type a name that will help you identify the group of pictures you will resize (picasa will create a folder with that name)
c:Image Size options. This feature allows you to specify the width of the resized pictures. The height will be adjusted proportionally. We recommend the width to be 640 pixels or less. If you are making thumbnails, they should be 150 pixels or less.
d:Image Quality. Lower quality will result in images that load faster. If you are not sure about this feature, just leave the default setting as it is.