There are actually five additional levels after level 70 which cannot normally be accessed unless you perform the following procedures. In Level 5, ram the wall to the left of where you start 5 times, then shoot the wall to the right of where you start 5 times. This will make a key appear; use to access the new path which leads to a warp panel to Level 71. The levels will continue as normal until you complete Level 75, which will then lead back to Level 61.
Locate a flashing wall in Level 1, then shoot it five times. If you turn around you should find that a new hallway has opened up. This leads to a secret area that contains five warp exits which will let you jump to different levels, plus you'll find 9 extra lives here for the taking as a bonus.
At the menu screen where you can choose to enter Cyberspace or the Arena, go into Options and change your name to "CONFIG_SYS" (without quotes). Press Start and you will gain access to the debug menu featuring a level select, starting equipment and number of lives, and more. Press Start again to activate the cheats and begin a game.
Hold L and R and press Start to select the number of players at the title screen. Continue to hold L and R until the screen turns black. Release the buttons to display at the interface screen. "Cyberscape" will now appear beneath Cyperzone. Select Cyberzone.