Maybe SLES 9 is ... old?
So if you really need a later version of gcc you should seriously thing about upgrading from SLES 9. If some library or app you wish to use specified a later gcc then it is likely to also require later versions of a few more things (which are more complex) ... and that's when you discover they need this and that and t-other versions which need this and this and that and the other other and that other thing there and .... >
Tell in more detail your "specific and urgent requirement" ... what app?
If you only needed a later version of gcc then download from source, configure, make and make install would probably work for you with a minimum of difficulty because of needing other software.
BUT I suspect because you need a later gcc you're looking at something which needs that (and is likely to need other later things which gets you into the package dependancy nightmare).
On the other hand, to answer the asked question:
If you wish to make things easy try to use the Suse GUI tools for upgrading software, don't try downloading & installing rpms directly. You're looking probably for Yast2 tool (yet another sys-admin tool). And Yast2 invokes YUM for package management and rpm installs.
BUT if SLES 9 is old and you want later versions of any packages this won't work. Newer packages will only become available for a few years for any linux flavour version.
After SuSE stopped making updates for SuSE 9.1 home then apt4rpm provided a good and easy way for getting updated packages for a while ... BUT ... it's quite old now.