I have turned even lesser laptops to a decent status by replacing the HDD with a ssd.
The result is magical.
My method of choice is to replace with a samsung ssd and use the samsung ssd migration app to do the move.
Since you may not have a second sata port available, you use a usb to sata adapter cable($10 or so) to do the move.
As to ram, cpu-Z will identify your ram specs and what slots you have available.
8gb is a good idea, but only if you are using a 64 gb version of windows.
32 bit is limited to 4gb.
If a second slot is available, buy a stick that matches as to speed, voltage, capacity.
Look at the ram upgrade app from crucial or kingston and enter the make/model of your laptop.
You should get a list of supported upgrades.
As to windows 10, you may not find old laptop drivers for 10 if the laptop never had a windows 10 option.
That said windows 7 drivers usually work.
It is the keyboard drivers and battery management apps that is mostly at risk as an issue.
I would not do w10 without the 8gb upgrade.
I would not try to upgrade unless there was some particular feature of windows 10 that you want.