How to do convolution for given data set

I have data set as given in excel sheet "convolution.xlsx" (attached) containing values of "y" vs f(y).

I want to do 4-fold convolution of f(y) like below

1st, f1(y)=f(y)*f(y)

2nd, f2(y)=f1(y)*f(y)

.......and so on upto f4(y)

and then I want to plot f4(y) against y

Now, which convolution (circular/linear) should I do?

How to do the convolution for this data ?

Kindly give me suggestion.

Thanking you in advance.pro