There are several ways to rid yourself of unwanted layers in AutoCAD LT.
First up, the Delete button in the Layer Properties Manager. This is useful when you only have one or two specific layers you want to get rid of -- otherwise it's a little tedious. You also can't delete a layer if it has anything on it, whether in the main drawing or in a block reference.
So if you want to delete multiple layers at a time, check out PURGE. It will go through your drawing and remove all unused layers, so you don't have to guess which ones might be eligible for deletion. Purge has a checkbox at the bottom to "confirm each item to be purged" -- unless you feel like clicking "OK" for every single layer to delete, you'll probably want to uncheck this.
But what if that layer just won't purge? It must have some geometry on it somewhere, or you could just delete it. But maybe those lines/arcs/whatever are hard to find, or nested in one of the hundreds of block definitions in the drawing, or...you get the picture.
You could use QSELECT to get all objects on that layer, and then purge or delete it, but if the only geometry on that layer exists in a block reference, this method won't work.
Instead, try two former Express Tools (LT 2007 and up): Layer Merge and Layer Delete. Layer Delete (LAYDEL) will blow away any layer you want, along with any objects that might exist on that layer. Using it is a little dangerous, since you don't ever get to see what was actually deleted.
Layer Merge (LAYMRG), on the other hand, combines your unwanted layer with another that's already in the drawing. The layer definition goes away, but any geometry that was on it gets moved to the other layer. So if I were to start the command, select layer HAM as the "layer to merge" and layer CHEESE as the "target layer" (hey, it's almost lunchtime), all objects on HAM would be moved to CHEESE and HAM would be deleted.
It seems to be popular to use layer 0 as the target layer, so you don't get any strange objects on your existing defined layers.