Each individual mod in a pack is organized in its own .jar file within the Wanderlust Reloaded folder. What you want to do is:
1) Download Wanderlust Reloaded v1.2.3 if you haven't already. Allow it to crash on launch, or kill it early with the console. Doesn't really matter.
2) Go back to the FTB launcher and highlight Wanderlust Reloaded (WLR) from the list. Click
edit mod pack, This'll show you a list of the mods active and inactive.
3) In the bottom left of the window that opened, there should be a button called "Open Folder"
4) Ctrl+F and look for the Chisel 2 file, it should appear as
Chisel2-2.3.5.31.jar
5) Now go here:
http://www.minecraftforum.net/forums/mapping-and-modding/minecraft-mods/2254671-chisel-2-2-3-5
Download the latest version of Chisel 2
6) The move the file you download into your mod folder. Delete the old one.
I hope that was clear, but tl;dr you want to replace the old Chisel2.jar with a newer chisel2.jar
Edit: Following Danidas' post, you can download a more-more recent Chisel2 version here:
http://coloredlightscore.us.to:8080/job/Chisel-2 v1.7.10-Dev/46/