The images that come with the maze game are 24x24 pixels.  If you have larger images for your maze blocks, spaces, and pellets, you need to change the size of the individual blocks in the maze code.  Open MazeGame.py and find the line BLOCK_SIZE = 24 near the beginning of the file.  Change '24' to whatever size your blocks are in pixels.  Note that your blocks MUST be square.

Since you increased your block size, you need to increase the size of the window to be big enough for your game.  Change the numbers in the line windowsize = windowwidth, windowheight = 500,575 to be the desired width and height of the window in pixels.  The game automatically centers the maze in the window.

The background.png file must be the same size as the window.