If you don't want to update to PSE 13, you could download/install the free Adobe DNG converter 8.6. Use the converter to convert the ARW files to DNG files which can then be used by PSE 10.
DNG Converter 8.6
Thanks for your help - I've downloaded the DNG converter, but when I open the folder in step 1 to select the ARW file it won't let me select any of them. Don't suppose you know why?
If not, they should work fine on PS13?
Sorry, I forgot to warn you about the way the converter works - it works at folder level.
The best idea to to place all your ARW files in a folder and you specify the folder to the converter not a file. You can specify that the converted files go to another folder if you want to.
When the DNG converter is prompting for a location, it is asking for the FOLDER. You choose the folder that contains your raw images, but you don't double-click on it. The DNG converter works at the folder level. When you choose the folder and click convert it will convert all the images contained in that folder and will place them wherever you choose to have them placed.
Thank you both for your help - that works great!