you can upgrade R on the instance using the standard "yum update" system commands.
However, updating R from 3.2 to 3.3 will result in your installation forgetting all previously user-installed packages, including DSS-installed extra packages, as the standard path for those includes the R version ($HOME/R/x86_64-redhat-linux-gnu-library/3.2).
The best way to upgrade is to replay the DSS "install-R-integration" command, which will reinstall all missing packages from scratch. You will also need to reinstall extra manually-installed packages if any.
If you want to cut corners, you can also try to rename the 3.2 directory above in 3.3, as most packages should-be upwards compatible and still work with the new R base version. Of course the result would not be officially supported but it has been observed to work.
Hope this helps