How to shoot in RAW format on Nikon d5100?
Please don't say look at your manual, because I lost it: c
Since you don't have the Owners Manual just follow these steps.
Step 1 - Google the information for the Owners Manual such as typing in Nikon D5100 Owners Manual
Step 2 - Click on the Link for the Nikon D5100 Owners Manual
Step 3 - Find the Page on how to change the Image Format to Raw
Step 4 - Follow the Steps of the Owners Manual
Look at Page 47 of the Owners Manual
http://www.nikonusa.com/...oprint.pdf
You can download a copy free from Nikon (you'll need a pdf reader if you don't already have one, but Adobe, Foxit and Sumatra are also free to download) - and reading it should ALWAYS be your first option.
I'd imagine there's an option in the menu where you set your resolution.
Once you download the user manual, look on page 48