In this window you may apply all-inclusive and irreversible changes to all product prices.
In order to get to “Global Changes” click on Store>>Manage Store>>Store Settings>>Global Changes.
In order to perform a comprehensive change, choose the price you wish to change, (list prices, or site prices) enter the amount, or percentage of the change, select percentage or set price, and finally, select a plus or a minus for increasing or decreasing the numbers respectively. To finish, click “Apply”.
For example, here you can see a price change for all products on the site, giving an all-inclusive set discount of 30%:
And here we are adding $10 to the list price of all products on the site: