euca-modify-instance-type: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/euca-modify-instance-type - from package: euca2ools

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/euca-modify-instance-type - from package: euca2ools

You may install the required package with command apt-get install {package}

Error in other languages:
euca-modify-instance-type: bevel nie gevind nie
euca-modify-instance-type: comandă negăsită
euca-modify-instance-type: comando não encontrado
euca-modify-instance-type: commande introuvable
euca-modify-instance-type: command not found
euca-modify-instance-type: käsku ei ole
euca-modify-instance-type: không tìm thấy lệnh
euca-modify-instance-type: komanda nerasta
euca-modify-instance-type: Kommando nicht gefunden.
euca-modify-instance-type: kommandot finns inte
euca-modify-instance-type: komut yok
euca-modify-instance-type: nie znaleziono polecenia
euca-modify-instance-type: níor aimsíodh an t-ordú
euca-modify-instance-type: no se encontró la orden
euca-modify-instance-type: no s'ha trobat l'ordre
euca-modify-instance-type: opdracht niet gevonden
euca-modify-instance-type: parancs nem található
euca-modify-instance-type: perintah tidak ditemukan
euca-modify-instance-type: príkaz nenájdený
euca-modify-instance-type: příkaz nenalezen
euca-modify-instance-type: команда не найдена
euca-modify-instance-type: командата не е открита
euca-modify-instance-type: 命令找不到
euca-modify-instance-type: コマンドが見つかりません