You have a couple approaches:
The most "popular" one appears to be to use the DNG "format". From Adobe you download the free dng converter that is current (that supports the 70D). In the converter, there is a setting to the version of Camera Raw that you are using. With CS4 and LR2, I believe that would be ACR5. You will also need to choose options for how you want your files to be handled. You then run your files through the converter. The resulting dng files can be opened by both Lightroom and Camera Raw (if you want to open them directly in Photoshop). I'd suggest that for this approach you make a backup of your CR2 files in your dedicated backup drive.
The second approach would be to use the Canon Raw processor Digital Photo Professional (DPP) to process your CR2 Raw files (not dng files). This approach has actually gained popularity over the years because Canon has improved DPP in numerous ways, in fact, you can potentially do your work in DPP and output final jpegs, similar to how folks like to use Lightroom, or for more work you can "transfer to Photoshop" where DPP creates a tiff file (similar to the default behavior of "Edit in Photoshop" from Lightroom).
The downside of using DPP is that you won't be able to use Lightroom with your Raw files. The downside of the dng conversion is that you won't be able to use DPP with the dng files. And, LR5 should be able to work with your CR2 files, assuming you want to go "back" from using dng!
If it were me, because I'm a "died in the wool" Lightroom user, I'd take the dng route. But I'd also say that you would benefit by saving your nickels and dimes for a newer version of Lightroom, either LR4 or LR5, because Lightroom has gotten some very nice developments through those two versions!