As long as you have root access to your debian machine, you can do this as follows:

/etc/init.d/mysql stop #stop MySQL
/usr/bin/mysqld_safe –skip-grant-tables & #start MySQL with --skip-grant-tables
/usr/bin/mysql -u root mysql #connect to mysql as root, straight into the 'mysql' database. No password is required
UPDATE user SET password=PASSWORD(’newrootpassword’) WHERE user=’root’; #Do replace 'newrootpassword' with something that you'll remember.
q #to quit
/etc/init.d/mysql stop #stop MySQL
/etc/init.d/mysql start #start MySQL

You can now test with mysql -u root -p you’ll be prompted for your password and your ‘newrootpassword’ should now work!