exhaust pipe

I have just purchased this wr450f jyacj04w0000 and the exhaust has been changed and is clearly not the right one, as you can see the first section is a lot smaller than the second so cannot be connected properly? Do I need a bigger front part or a smaller back part? Thanks in Advance

Hey guys, I'm wanting to replace the exhaust on my 79 XL125 with the same setup in the photo. I already have the muffler, just need the pipe. Anyone know where I can get it? Thanks