As reported by many websites, the HD of the MacBook can be easily changed by an end-user, as it is already the case for the RAM modules. It is indeed the case as shown by those photos:
First, remove the battery:

Then, the metal part covering the access to both RAM slots and HD:

You can now see the HD and a white strip with which you can easily pull out the HD:

Here is the HD:

You need to ensure that replacement HD does not void the warranty (which is unlikely). Replacing the HD is quite easy to perform. The MacBook, as its brother the MBPro, uses 2.5" SATA HD.
Other photos of a MacBook disassembly are available from our friends:
Kodawarisan.
JCJ