Take backup of your existing Koha database.
Apply the following command in a Applications > Accessories > terminal,

sudo su
mysqldump --single-transaction -u root -p koha > koha.sql

Copy your backup in a pendrive.

Install Koha either using Koha Live DVD / manual installation

Upgrade Koha installation

apt-get update

apt-get upgrade

apt-get install koha-common

Koha Database Restoration process.

Open a terminal and apply following commands.

Remove existing database in new installation

sudo su

mysql -uroot -p

[Enter the MySQL Root password]

drop database koha_library;

create database koha_library;

quit;

Copy your database backup from your pen drive to home folder.

Then restore the old backup to new installation.

Database Restoration command,

mysql -uroot -p koha_library < koha_library.sql     [Check name of your source Koha database] 

koha_library - name of database in new installation

koha.sql - name of database in old installation

Enter the MySQL root password.

Upgrade Database Schema

Database schema of old Koha should upgrade to new one. Apply following commands in a terminal,

sudo su

koha-upgrade-schema library

Then rebuild the Zebra Index.

Apply following command in a terminal,

sudo koha-rebuild-zebra -v -f library