To actually change the server tokens you need to recompile, but you can turn them off with the ServerTokens directive.

Unfortunately, “[the] setting[s] appl[y] to the entire server, and cannot be enabled or disabled on a virtualhost-by-virtualhost basis.” Which means it must be used in the main server configuration files. Some ISPs can be convinced to turn them off completely on a security basis — other than that you’re out of luck.