Your information is not enough to really offer you an alternative to the interface. However, can I answer your question with a question? Why do you think you should change it? Did your customer complain? If not, it looks like your client is happy with how the software works right now, so I would not change it. If your client complains about this, he will most likely not just say “This is bad”, he will say “Why he cannot look ...” and this will give you an idea of how to change it.
I had to redesign a very outdated product management system. The old one was written for an already dead database system that still works on MS-DOS. The client suggested that I create a prototype of what this re-implementation might look like, and then he will decide whether I get this job or not. I replaced the old, dead database with a modern MySQL database, I replaced the problematic shared peer-to-peer access using the client server approach, and I decided to rewrite the user interface in Java, as different OSs were used, and this had the lowest migration cost. While the concept seemed good, the client liked it. However, when he asked his employees what they think about it, they asked: "So far it's great, but we have one question: why does it not look like the old one?" In fact, it turned out that even with all the modern technologies, they wanted the interface to look and manage exactly like the old one. So I had to rebuild the 1986 MS-DOS usability nightmare in Java because no other user interface was adopted.
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