upgrade PHP

There is PHP 4.2.2 in my liux sysem. I want to upgrade it. I have downloaded the php 4.3.9 version. How to upgrade it? Do I need to uninstall existing PHP and then install the new version? Then how to do it?

I downloaded PHP4.3.9, configured. but it has following errors:
loading cache ./config.cache
checking host system type... s390-ibm-linux-gnu
checking for gcc... gcc
checking whether the C compiler (gcc ) works... yes
checking whether the C compiler (gcc ) is a cross-compiler... no
checking whether we are using GNU C... yes
checking whether gcc accepts -g... yes
checking whether gcc and cc understand -c and -o together... yes
checking how to run the C preprocessor... gcc -E
checking for AIX... no
checking if compiler supports -R... no
checking if compiler supports -Wl,-rpath,... yes
checking for re2c... exit 0;
checking for ranlib... ranlib
checking whether ln -s works... yes
checking for mawk... no
checking for gawk... gawk
checking for bison... no
checking for byacc... no
configure: warning: You will need bison if you want to regenerate the PHP parsers.
checking for flex... lex
checking for yywrap in -ll... no
checking lex output file root... ./configure: line 2425: lex: command not found
configure: error: cannot find output from lex; giving up

what's problem?


Thank you

It means you have not lex command on your system.
You need to install it
visit
http://packages.debian.org/stable/devel/flex

http://howtos.linux.com/guides/html/appendixa/flex.shtml