You can follow the steps given below to install yasm from source.
# wget http://www.tortall.net/projects/yasm/releases/yasm-0.7.0.tar.gz
# tar zfvx yasm-0.7.0.tar.gz
# cd yasm-0.7.0
# ./configure
# make
# make install
You can check the yasm binary using the command
# which yasm
/usr/local/bin/yasm