The acer uses DDR3 1066 and the Dell DDR3 1333, both only have 2 slots available which is normal for notebooks. Dell, well most OEMs, tend to fill both of the available RAM slots as well. You didn't list how much RAM you currently have in the Dell, however it can support 4 GB DDR3 1333 204 pin modules, although it says it supports a max of 6 GB, that seems odd but OEMs love to have artificial bios limits that make upgrades a hassle.
The Dell only has 1 hard drive slot, so likely won't be worth swapping them out unless you actually are out of space and that 500 GB is larger than the current, but this would involve reinstalling OS, programs and files etc, likely also not worth the hassle.
I'll also add that you could purchase a USB harddrive enclosure for the acer drive and use it as external storage and get access to any files you might need off the drive.