Open following file in your favourite editor :-
$CATALINA_HOME/conf/tomcat-users.xml or
/usr/local/jakarta/jakarta-tomcat-4.1.31/cinf/tomcat-users.xml
and append the following line at second last line.
<user name=”Username” password=”secret” roles=”admin,manager”/>
Restart tomcat .You should be able to login to tomcat with
http://IP:8080/manager/html