Landscape Texture size not changing?

I imported a texture not noticing it was 256 so I changed it to 1024 and reimported, however on the landscape it’s still the same size ?

The way a texture is sampled for landscapes is the “LandscapeUVCoordinates” material node.
The native resolution of a texture is independent from the sampling in world space…

So any size will still be per square unit ?

If you import squared textures (for example 2048x2048), they will always be squared on a landscape. If you want to change it, you put a “LandscapeUVCoordinate” material in front of the texture. Then you can change the U and V tiling (or x and y) to make it non-squared for example. If you want to change the size, normally you multiply the outcome of “LandscapeUVCoordinate” with a scalar parameter, make an instance of the material and tweak the scalar parameter.
Further information about how to make terrain and the material for it, can be found in the documentation: Landscape Quick Start Guide | Unreal Engine Documentation