The fuel filter is considered to be a maintenance free but periodic inspection is recommended. Depends on fuel quality. If there are some important safety matters like fuel flow restriction, surging, loss of power, hard start problem etc, replace the fuel filter immediately regardless of maintenance schedule and consult an authorized KIA dealer for details.
Removing the back seat is not too hard
2 bolts in the back of the bottom seat, two pull tabs on the front part pull up, *they are hard to do*
*too get to the seat bolts you just need to open the trunk and pull on the two handles so you can lower the seat backs.. thats it..
But I don't remember seeing the fuel pump lid while I was back there.. I think it might be in the trunk.
Not that you really need to worry about that right now anyway
It depends on the quality of the fuel. If it is a good one, it may take two to three months but if its not, it should be replaced after a month. It is considered to be a maintenance free but periodic inspection is recommended.