After you've been using the laptop a while right-click the Windows task bar, and click "Start Task Manager". Click on the Performance tab.
The lower left graph is of your physical memory vs. how much is being used. If it's over about 3-3.5 GB, then you can probably use a memory upgrade. (Assuming you have a 64-bit version of Windows. Click the Start button, right-click on Computer, click Properties. The window that pops up will tell you if you have a 32-bit or 64-bit OS under "System type".)
That said, I would still recommend a SSD upgrade, especially for a laptop. Most laptops use slow 5400 RPM drives, some use ridiculously slow 4200 RPM drives. A SSD makes a huge difference in system responsiveness. The only reason I can think of to hold off on these upgrades is if you want to just get a new laptop. Most SSDs come with software to help you clone your existing HDD to the SSD (if you don't have an external USB enclosure, then buy one, or pay the extra $10-$15 for the upgrade kit version of the SSD which has it). You basically put the SSD in the enclosure and plug it into a USB port, boot off the cloning CD/DVD, have the software clone your HDD to the SSD, shut everything off, then swap the SSD and HDD. It can also be done within Windows if you don't have a CD/DVD drive, but there's a slightly greater chance it won't work. If the drive didn't come with cloning software, you can use free ones like Clonezilla.