Click the Edit button with the pencil icon on the right side of the option box.
When editing an option, you can manipulate any of the data fields you like (description, desk count, price, etc).
Any edits that you make will only affect the option on this particular opportunity (for example, changing the price of Office 1 from $1000 to $900 will not change the price of Office 1 on any existing or future opportunities).