broken cord on a briggs & stratton 3.5 gas mower?

I would like to know if there isn't a special tool used to remove the odd looking bolts on the top of the mower. I am a 61 yr. old female & do not have the funds to pay a pro, and I know I can do this. I just need help and instructions, so, can you please help me, and the sizes of the tools needed to replace the broken cord, that is causing my mower to be inoperable. I do not have a lot of tools within my collection, so, I definitely do need some assistance.