I need to change out my 3-prong power cord on my Inglis dryer?

I need to change out my 3 prong cord for a 4 prong cord on my Inglis Citation dryer(circa 1970s), I believe the model number is 1ED 3572B67. I know HOW to do it, my problem is, I have no idea how to access the terminals! Where the power cord comes out from the dryer, there is a little panel held on by screws, but we can't get it to come off, AND even if we did, there is only a very small hole where the cord comes out...not big enough to work in. Do we have to remove the whole back of the dryer??