The phrase "allow them to upgrade" is correct and usable in written English.
You can use it when giving permission or enabling someone to enhance or improve something, typically in a technological or service context.
Example: "We need to ensure that our users can access the latest features, so we should allow them to upgrade their accounts."
Alternatives: "permit them to upgrade" or "enable them to upgrade."
Big member states, such as Italy, tend to defend the interests of their big telecoms firms, which argue that only profitability will allow them to upgrade their networks.
Independent designers and architects are appealing to the style-conscious homeowner by launching products that allow them to upgrade and customise the most popular lines from the world's largest furniture retailer.
This project attempts to address new development strategies through the application of design methodologies and the use of CAD (Computer Aided Design) technology in the craft manufacturing process, aiming at optimising processes and at providing craftsman with resources that allow them to upgrade and improve their production systems.
This would allow them to upgrade to newer hardware and keep their car.
And don't forget all those pour souls in corporate jobs who are forced to use the browser because their IT departments won't allow them to upgrade.
While this might not jump out at you as a huge thing, it's big news for millions of users stuck working at offices or schools with older machines where admins won't allow them to upgrade to newer, modern browsers.
It offered customers the iPhone and other popular models and allows them to upgrade their phones every six months.
Beyond simplifying installation, this also allows them to upgrade and maintain the application remotely by modifying the site, without any sort of manual upgrades required on the hotel's end.
Executives at a number of nonprofit groups say that the weak Manhattan office-leasing market is allowing them to upgrade their office spaces significantly and negotiate rents that would have been almost unthinkable a year ago.
[C10.] Nonprofits Find Space Affordable Nonprofit groups say the weak Manhattan office-leasing market is allowing them to upgrade their office spaces and to negotiate rents that would have been almost unthinkable a year ago.
