There are no optional motherboard replacements for laptops since a motherboard is specifically designed for a specific notebook chassis. In other words, there are no standard size.
If you have no use for the laptop, then either re-gift it to someone else, or sell it and use the money towards buying a laptop that suits your needs or a desktop.
The fastest AMD E series CPU is the dual core E-450 @ 1.65GHz which may or may not be recognized by the laptop's chipset. However, AMD E series CPUs are only sold to OEMs to the best of my knowledge which means you cannot simply buy it yourself online unless you attempt to purchase them in lots of 1000 directly from AMD. Of course that means you must become an authorized AMD business partner to do so.