Help needed please -The screen on my laptop just enlarged itself ??!

[conserve]

I just rested my hands down and must have pressed something.
Im struggling with Excel (thats a whole other thing) so am scared to touch anything to bring it back to normal size. The cells are huge and its making it very hard to work as I can no longer see the whole sheet.
Could someone please advise me on what I need to do. I have tried looking on google but theres too much out there and I have great faith in the powers of Mumsnet. I have Windows 7 if that is relevant?

Try pressing CTRL and the minus key

I tried that whilst on the spreadsheet and it had no effect but it worked when on the Mumsnet page (so outside of Excel).
I eventually found the scale button for Excel and have managed to do it that way. Emily is CTRL and - just to make the screen larger/smaller?