I think you'll see a big performance improvement switching the mechanical HDD to an SSD, in addition to upgrading memory to either 8GiB DDR3L or 16GiB DDR3L.
+1
Tried and tested on a Lenovo G410.
Get at least a 240GB SSD. Kingston or WD Green are cheap online. They're not the best in terms of speed but any SSD will leave your current HDD in the dust. Put your old HDD in a USB enclosure as additional storage.
For the RAM, getting it up to 8GB should be enough. From experience, it's more than enough to handle 2 instances of Chrome with multiple tabs each plus an additional Firefox browser.
If the laptop is used for work from home, consider getting an external keyboard. Not only will it make working easier, it's also easier to replace than your laptop's keyboard.