Updating Website Product Prices
First, go to Products > Products > Website Products.
Find the product you want to update and enter the new price in the box under the Price column. Hit Save on the product record (or Save All at the top of the screen if updating multiple products) and you're done!
You can use the category tree on the left (click a category title) to narrow the products you're viewing down to only the selected category.
Updating POS Product Prices
For POS products, go to Products > Products > POS Products, change the number in the price box, and hit Save at the end of the row.