There is no patch from 1.7.4 to 1.7.6 because the patchfile is considerably
larger than the whole 1.7.6p0 distribution. 

Users of 1.7.4 are advised to compile a clean 1.7.6 tarball distribution
and transfer their files there, as described in the file UPGRADING
in the 1.7.6 distribution. If you have local hacks, you will have
to apply them back to 1.7.6 (or try to make a diff from stock 1.7.4
to your 1.7.4 and patch that in).