Not worth it, unless you're prepared to change operating systems. I recommend you sell the entire system intact and build your own. Dell, acer, and hp aren't designed for upgrading the cpu. It's a crapshoot, but you can try it if you like.
Overall, it's not worth the expensive to upgrade a laptop. They really don't design them to be upgraded easily. When my laptop died a year ago, it was cheaper to buy a new one than try to order the motherboard. I couldn't find a motherboard for cheaper than $400.