Since you are using SuSE, you should have d/l'd an rpm of the gcc package. Upgrading SuSE would then be as easy as "rpm -U <packagename>" to upgrade an already installed package. But, since you chose instead to compile a source package, there is no way to upgrade the already installed package. You will end up with parallel installations of gcc. Figuring out how to tell other packages how to use the new gcc give me a headache just thinking about it.
If you insist on using source packages in SuSE, at least, get the .src.rpm (source rpm) and build an installable binary rpm for SuSE from that.
If you must do it the hard way, with tarballs, please consider using stow or encap to ease the process. Both will create a directory in /usr, into which each will install source packages, each in it's own sub-directory. When you want to upgrade a source package using either of those applications, each will check the already installed package under its control, and upgrade to the new source package.
Note: each will only work for its own sub-directories, and not for sub-directories created by the other!