Can I safely increase the size of a fuse?

I have a 1991 Mercedes 190E.
I want to use my Tomtom One/XL together with my Cobra gatso detector in a 'two-into-one' adaptor/ converter plug. When I try this the (16amp) fuse blows. I have a 16amp fuse as this car has an electric roof. (If this car does not have an electric roof the fuse is only 8amp).
Can I SAFELY increase the size of the fuse in my fusebox? Or are there any alternatives while using both devices, or indeed a phone charger or whatever?
I am very concerned that I do not ask too much of the original wiring on this 19 year old car, as it is my pride and joy.