Can I use a higher voltage rating when replacing capacitors?
The bad caps are both 6.3 V, 4700 µF and i was thinking of replacing them with 16 V, 4700 µF


Yes, you can pick a higher voltage without problems.


  but getting the better quality 105 °C rated one as the others ones are 85 °C rated.


Again, yes, 105°C will last longer.

HOWEVER:

These caps are most likely at the output of a switching power supply (please check). In this case, you will have to use low-ESR (or low-Z) models rated for this use. 

Consider Panasonic FC-FM-FR, Rubycon ZL, for example, but do not use "general purpose" caps in a low-Z position.

Also, please make sure the capacitors fit in the holes. Don't connect them with wires or stuff like that, as the extra inductance could increase HF ripple from your switching supply.