No, those temps are fine. I would start getting concerned if your GPU starts to reach upwards of 70°C.
Yes, you can underclock your GPU, but considering that the 250s aren't exactly top notch cards, why would really want to make them perform worse? GPUs can also be equipped with an aftermarket cooler. Here's a good one: http://www.scythe-usa.com/product/vga/002/scvms1000_detail.html