It might not be cost-effective to even attempt something like that. The price you'd pay for all the parts and labor would be more than what your laptop is currently worth, I think. And even if you did that, Dell charges a huge premium for their parts (meaning non-warranty components). If you even went with a non-Dell motherboard then you would have to factor in the cost of buying a copy of Windows since it will not reinstall on a non-Dell motherboard.
If I were in your shoes... I would search around to see what the selling price is for my laptop on a few sites and put it up for sale or place a few ads. While that was going on, I would price out some new (or even used) laptops that fit within the parameters of what I'd like to have... i7, 16GB RAM, kickbutt integrated GPU... and buy or order it as soon as I sold the laptop.