Using the Product List to make mass updates on pricing
If you want to increase or decrease your prices, you can use the Product List, to do this.
Go to My Site > Product > Product List
Click the top box in second column to select all products.
Click Edit in top hamburger menu.
Within the pricing section, Click the checkbox next to price 1 and then set a price for price 1, using the data form instructions.
Here are the pricing options that you can set for the price. (X = the price of the product)
X - Changed current price to X
++X - Increase the current price by X
--X - Decrease the current price by X
++X% - Increase the current price by X%
--X% - Decrease the current price by X%
In the example below we've upped the price by 10%