Replace 5 speed box with 6 speed?

Hi Guys & Gals
Just joined the forum and looking for some help
I have a very good 2001 Movano van with only 88k on the clock, we are converting her into a day camper as we have some very large dogs
I would like to know if it is poss to change the gearbox from the 5 speed to a 6 speed?

Thanks for your help in advance

Blue