Problems to update to

Good afternoon, along with greeting and I hope you are well, I tell you to update to, for that I had to update debian 7 to debian 10, php from 5.6 to 7.3, from mysql 5.5.58-0 + deb7u1 to 10.3.18-MariaDB-0 + deb10u1,but I have two drawbacks:

*the main interface looks different from how it was (it’s the second time I updated it and the first time it hadn’t happened)
*The second problem I have is that I cannot configure the postfix, when running “postmap /etc/postfix/sasl_passwd” the following error appears: “bash: postmap: orden no encontrada”

could someone help me with this problem?