In WryeBash all I see is "update.esm". Is that it?


I want to disable it because I just want to use Skyrim HD from the Nexus.

No, it's not. If you haven't explicitly added the DLC to your account, then you won't have them

I downloaded the DLC, but then I looked at some screenshots and I liked some Nexus textures better.

How can I get them to load over the DLC ones (do they even load over the mod)? Can you delete DLC? (I'm a Steam noob)

If you downloaded the DLC, you'll have ESPs that are called something like HiResTextures or Textures or something related to that. May want to look in the Data folder. If you don't see them, you're good to go. If so, and they aren't showing up in the Data Files menu, you may need to verify your files to make sure nothing is wrong. If they do show up there, just disable them.

The High Resolution Pack drops two ESPs into your Data folder, which you should see in Bash:
HighResTexturePack01.esp and ...02.esp.
AFAIK the Skyrim Launcher enables all ESPs in the Data folder by default, so you should check if they're checked when launching the game. To be safe, just move the ESPs out of the Data folder.
If the ESPs are disabled, the DLC won't be loaded.
For having both the DLC *and* custom textures overriding it, check http://www.gamesas.com/topic/1344060-guide-using-custom-textures-with-the-new-highres-pack/.