Please do not go for any upsize. It is a very tricky business, especially for two-wheelers. You must inderstand that bikes are inherently very prone to accidents ( due to the design and balance ) and any change in tyre size can adversely impact the handling and riding characteristics of your bike. Please stick to the stock size only.
If you are not happy with the performance of the current tyres then invest in better tyres but in the stock size only.