A print screen of the node graph would be welcomed and informative.
The
Gradient Map node is basically a remap node with support for color information, unlike the
Range node which is also a viable and similar node but differs in some aspects.
A go-to node for altering textures (procedural or disk files) is typically the Gradient node in its simplest default configuration with a few tweaks such as moving the extremities (black and white) position, changing the greyscale value/inverting it and/or adding more greyscale values in between the extremities.
What could go technically wrong is more often than not related to file textures color space, as covered on
this page.