With Picasa you can easily decrease the size of multiple pictures or a full folder of pictures you clicked with your high resolution digital camera.
Here are the steps :
Step 1 : Import the folder in Picasa. The Import button is found on the top left corner of the screen.
Step 2 : Now click the Export button in the photo tray which is in the bottom of the screen.
Step 3 : Once you click the Export button, Export to Folder window pops out. Select the Export settings like export location and export folder name.
Step 4 : Also you can customize the image size and quality.
Step 5 : Finally click on Export.
The exported images will be stored on your hard drive at the location you specified. Also those images can be found in the Exported Pictures collection in Picasa.