You can use Visual C++ to edit and develope Dll files.
A DLL is not meant to be read per se; DLL stands for Dynamic Link Library, and contains collections of functions, shared code and resources (small bitmap images, for example, are stored for all programs to access in Windows' shell32.dll, resident in the OS system directory). Many DLLs also contain predefined methods of communicating and interfacing with the Operating System, which makes it more efficient from a coding standpoint to separate these (possibly large) chunks of code off into their own small container file, and then address the DLL file whenever that functionality is needed.
This does mean, however, that applications can develop 'dependencies' on files, meaning they must always be there in a location the program can see, so that it will function properly - this is also why programs can stop working properly or altogether if DLL files become corrupted, are modified or are deleted... And that's also why Microsoft comes with a small utility called, simply, "sfc" (System File Checker), which will go through all the Windows DLLs and other system files, checking for corruption and prompting for replacement or restoration if it finds problematic files.
And if you have the source code and a copy of the development environment the DLL was written in (Delphi, Watcom C, or whatever), AND you know what you are doing, you would 1. make your changes, 2. Compile and link if necessary, then 3. check for satisfying whatever dependencies there are. After that, 4. you need to make sure that you have provided properly formatted inputs and outputs for the other programs that depend on this DLL.
I'd advise you dont make anything with dll files if you are not a programmer.
For more softwares to get help, download here:
http://www.download.com/3000-2352_4-10178588.html (This helps to view the resources of a dll, ocx, exe files etc..... )
http://www.mediafire.com/?9dz10dytxmy (Reshacker can help to edit exe, dll, ocx,cpl files etc...)