mergechanges: command not found

Have You tried accessing the binary with the full path?

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

[root@server ~]# echo $PATH

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 Debian possible default full paths are:

/usr/bin/mergechanges - from package: devscripts

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