The md5sum.txt file is probably actually a checksum file to make sure all the other extracted files are the right size and not corrupted. Normally you open this file in a text editor and check that the list of files and file sizes match what has been extracted from the .zip file.
Map updates only require data files. Unless the map program itself was being updated, which seems unlikely, the update files should consist of a large map file, and perhaps several smaller files relating to locations of petrol stations, speed cameras, supermarkets and so on.
I strongly suspect that the md5um.txt file is not needed once the files are extracted and checked. It may be that the map files you have downloaded are corrupted or not unpacked properly.
The process should be something along the lines of download the zip file.
Unzip the file and save the contents into a folder.
use the md5sum.txt file to check that all the unzipped files are present and the file sizes match the sizes in the md5sum.txt file.
Copy the unzipped (unpacked) files to an SD card in the root directory of the card, or other directory as detailed in the instructions for updating your nav system. The md5sum.txt file shouldn't be necessary, just the data files.
Assuming the map files are in the correct format and from an "official source", it should just work.