In essence you can't - not "natively" anyway.
You can either upgrade to Lightroom 6 (assuming that 6 supports your camera - you didn't say which one); or you can convert your camera's files to DNG using the Adobe DNG converter, and Lr 5 will read those.
Thank you both. The new camera is 5Dsr, and the link says I need LR 6.
So I tried importing the files by using the “Copy as DNG” option, but LR says “the files are not recognized by the raw format support in LR”.
Is there a way to convert the files to DNG outside of LR and then import into LR?
Download link for DNG Converter to covert your files to DNG and then you can import them to Lightroom 5:-
This solved my problem - thanks!