I do not know that article and the forum's search functions does not seem to work.

If the persistent image file is unencrypted then one can make use of the e2fs utilities. My method is to boot the live CD since a filesystem to be resized may not be mounted, to find the persistent image knoppix-data.img, to check the filesystem inside the container, to enlarge the container by adding some bytes to it and to resize the filesystem.

1. Open a root terminal.

2. Mount the drive with the persistent image

3. Change to the directory with that persistent image

4. Make a backup of the persistent image.

5. Check the ext2 filesystem and allow corrections
Code:
e2fsck -fy knoppix-data.img
6. Add 100 MB to the container
Code:
dd if=/dev/zero bs=1M count=100 >> knoppix-data.img
Remember that the maximum filesize of the FAT32 filesystem is 4 GB. Therefore the filesize of the persistent image may not be made larger than the maximum filesize of the underlying filesystem. Be careful, use ">>" instead of ">"!

7. Resize the filesystem.
Code:
resize2fs knoppix-data.img
8. Shutdown the system and boot Knoppix the usual way.

But if the persistent image is encrypted I think the only way to get a larger persistent image is to create a new persistent image and copy the data from the old filesystem to the new one.