Better to get the GNU version of sed for windows. Talking about replacement, many tools can be used, including Perl
perl -pe 's/abc/def/' myFile.txt
Similar syntax, accept Perl does a lot more. Even not with Perl, awk is also a better suited tool to use than sed, because awk is a nice little programming language. There's no point learning sed nowadays because what sed can do, awk can do, and it does more as well.