If it's like mine with the small front sprocket it's easy and inexpensive to change to a bigger one which for the same speed will move the chain on to the bigger cogs.
I have just done the reverse.. I never used the top two gears with an 18 up front so changed to 15 and now I do.
I have just done the reverse.. I never used the top two gears with an 18 up front so changed to 15 and now I do.