What should i upgrade first from my laptop?

RAM isn't a bad idea. What sort of storage device do you have on there?

What's your laptop model?

Can try this,

Download hwinfo32,
http://www.hwinfo.com/download32.html
open it,
click run,
close the top window which is the system summary,
click save report at the left top,
in the next window at the bottom check=dot "short text report" after that next,you'll get to see what is in your pc

Click to expand...

Looked and in the system summary at the left bottom is it also displayed.

Ram is not always as compatibel as you'd think so might just get a 2x4 set and keep the one you have as back-up or sell it.Something to read about it,
http://www.tomshardware.com/reviews/ddr-dram-myths,4155.html#p4
look at "Just Add More DRAM".

Can try this,

Download hwinfo32,
http://www.hwinfo.com/download32.html
open it,
click run,
close the top window which is the system summary,
click save report at the left top,
in the next window at the bottom check=dot "short text report" after that next,you'll get to see what is in your pc

Click to expand...

Looked and in the system summary at the left bottom is it also displayed.

Ram is not always as compatibel as you'd think so might just get a 2x4 set and keep the one you have as back-up or sell it.Something to read about it,
http://www.tomshardware.com/reviews/ddr-dram-myths,4155.html#p4
look at "Just Add More DRAM".

The model number of your pavillion is probably on a sticker under the battery - it would be helpful to know what laptop you're working with.

Oddly, I didn't find your exact model - but one that is very close to it (HP Pavilion 14-ab166us) wants
DDR3 PC3L-12800 204pin CL=11 DDR3-1600 1.35V SODIMM
It seem it will accept up to 16 GB of Ram - so you want either 2 4GB sticks or 2 8GB Sticks
As Vic 40 mentioned - it is safer to get 2 new matched sticks than to try and match the stick you currently have (you can probably easily sell your current stick) but you could .... buy a single 4 or 8 GB stick and give it a go (odds are, all will be good) - if the new stick doesn't want to work with your current stick - order another (matching) new stick. The important thing here is to get ram in each slot to improve performance (2 2GB sticks will perform better than 1 4GB stick and 2 2GB sticks will perform better than 1 4GB stick - if you get my drift.
You never actually mentioned what was motivating your upgrade so it's hard to give advise as to how much new ram you should get. I run an older pavillion than yours with 16GB (2 X 8) but I have to say - I never come close to using it all. But then, I don't do anything ram intensive like video editing etc.
If it were me, I would order 1 8GB stick - if it worked (it most likely will but don't quote me lol) with the current Ram - that would be great (you'd have 12 GB of ram) - if it didn't, I would bite the bullet and order the identical 8 GB stick (note that buying 2 single 8 GB sticks is probably going to be more expensive than buying a dual kit from the getgo - plus there would be 2 shipping charges). What can I say - life is a gamble - the choice is yours but ... you definitely want some working ram in both slots. Brand wise - Crucial seems to work well with pavillions.

Apart from the Ram - looks like quite an ok laptop (better than anything I use) - Having USB3 is nice and the hdmi port an added bonus. Oh .... but in your 1st post you say Processor (4 CPUs) - I'm not sure what is meant by this but ... I think your processor is dual core ... not a quad core. You could maybe think about a quad core update but ... do the Ram 1st and see what you think.

In the partslist made by hwinfo is info about the ram as well,could maybe find a matching stick with that.Again whether they work together is a gamble.Buying 2x4gb would be a better option,or 2x8gb.
Sets of ram are sold together for the reason that the maker is absolutely sure they work together,with adding one can there be compatibility issues.Then again they just might work together fine.

Adding a gpu to a laptop like this is probably not worth it,if it can be done (which is an issue anyway) would it be a costly one and imo not worth it.

Your hdd is a slow 5400rpm one from what i find,which you could change to an ssd if you wanted more speedy loadtimes and nice responsiveness of the system. Depends if you need the whole 1tb storage space of the current drive,a ssd of the same size is pretty high in price and imo not worth it.