Can you go and measure the outside of your 4.4 tips and I will tell you if those 4.8is tips fit over yours and will tell you exactly what job needs to be done for you to fit them

The 4.8is tips measure 15 x 6 cms inside and they should fit over you existing tips.
As has been said,you will need to weld them.

This is what I have done on some customers cars.
1.Cut the existing 4.4 tips about 7 cms from the rear of your silencer
( Keep these as you will be able to sell them and get some money back )
2.Make 2x stainless plates for the back of the 4.8is tips,with 2 holes to cover your existing tips (now cut)
3.Weld the plates to the back of your 4.8is tips
4.Disconnect the battery, or connect to battery terminals a peakstop electronics protector(I have this but I feel safer to disconnect battery terminal)
5.Slide the 4.8is tips (now with the welded plates)over the existing cut tips and once you get them straight ,just spot weld(just 2 welds) on top and side.
Confirm that both tips are straight and how you want them.
6.Spot weld them with 2 more welds on bottom and side.
7.Remove silencers and fully weld for a good seal.
8.Spray the weld with UHT paint and re-install the silencers and you are done.