Can the owner who benefits from an easement expand how they use it beyond what was originally granted?

Generally, no, not without agreement or a fresh legal basis. The owner who benefits from an easement, the dominant owner, is limited to using it for the purpose and to the extent that was actually granted, or, for an easement established through prescription or implication, to the extent and character of the use that originally established it. Significantly expanding the manner, intensity, or purpose of that use, for example, turning a pedestrian footpath easement into a driveway for regular vehicle or heavy equipment traffic, goes beyond what was actually granted, even though it's the same physical strip of land.

The servient owner, whose land is burdened, has real grounds to object to this kind of expansion, since they only ever agreed to, or had established against them, the original, narrower use. Courts look at the original grant's wording, or the actual historical pattern of use where the right arose through prescription or implication, to decide whether a given use fits within or exceeds what was established.

If your needs have genuinely changed, say, from occasional foot access to regular vehicle access, the proper path is negotiating an expanded or new easement with the servient owner, documented and registered, rather than simply starting to use the existing one more intensively and hoping it goes unchallenged.