I don't have a 707 but do have a 530-2 Record. Unfortunately, with some of these older machines, Bernina did not provide a very good method for accessing the light bulb. On later machines, the side cover would either be hinged or removable. If yours doesn't have this capability, the only way of changing the bulb is by reaching in with your fingertips, gripping, and turning the bulb to remove it and then installing the new bulb in the reverse manner (difficult for someone with big fingers). Sometimes it helps to use thin rubber gloves (like the surgical type), lightly moisten the finger tips to provide more "grip." There is also a sewing tool available that is somewhat like a pencil with a rubber suction at the end made specifically to help with replacing sewing machine bulbs. If you are creative, you may be able to fashion something similar.
Have you tried LED bulbs? I've installed them in all my Berninas. They provide a lot more light and do not get as hot as the regular bulbs--as well as, they supposedly last much longer! They seem expensive at the outset but if I never have to change a bulb again, so much the better!
In case you need it, here is the manual for your machine:
BERNINA Sewing Systems