The fix comes nearly 10 months after the Health & Safety Executive (HSE) warned that unclear screen displays at the Swanwick centre might not meet minimum legal standards.
Details of the changes were revealed by Colin Chisholm, chief operating officer at Nats, in an exclusive interview with Computer Weekly, in which he conceded that some controllers had concerns about the clarity of some screen displays.
He said the software fix, which was due to be installed in the early hours of Thursday morning, would enlarge and improve the definition of characters and numbers on screens.
"I am pleased to say we have not ended up in a sort of quasi-legal fight with the HSE about this because it does not help us. [The HSE] has acknowledged that what we have done makes an improvement," he said.
When the Swanwick New En Route Centre went live in January controllers complained of difficulty reading aircraft heights and other information on screen.
Meanwhile a new survey on ergonomic issues at Swanwick says that 76% of 300 controllers who responded had experienced eyestrain, 50% had suffered headaches, and 36% found it necessary to take medication during or after a work shift.
Chisholm criticised the survey, which was carried out by Swanwick's health and safety representative, saying the framing of the questions had been "incorrect".