Changing 23mm tyre to 25mm - considerations?
The two things to consider when increasing tire size are compatibility with the rim width and frame/fork clearance. Inner tubes fit a range of tire sizes. 

15mm rims will easily take 23 or 25mm tires. Check that your frame has sufficient clearance for an extra mm or two on either side (some tires are a bit wider than specified width) at the brake calipers, fork crown and chain stays. I'd be very surprised if the frame does not have clearance for 25mm tires.