What no guru said. 4 gig would do the trick , but it's border line. You'll have to adjust your workflow to work with the little memory. That means you'd have to close stuff down if you have too much open, bounce stuff, ad the bounce , delete the instrument, etc. IMO, workflow shouldn't be limited by something so superficial. There's already enough stuff limiting our workflow.
8 gig will give you a lot more room to not have to adjust your workflow. Anything more then 8 will give you even less to worry about.
You can see if you can upgrade the ram with the shop you're buying your laptop with. Sometimes, on pre builds, they can choose to resell your old ram and selling you new ram, costwise the most effective for you. Usually no build charge either. Replacing ram is about 5 minutes, testing 5 minutes. Do check the cheapest retail price on that ram though, sometimes it can cost you a lot more having the laptop reseller do it, sometimes not.
Otherwise, you can buy the ram yourself and put it in yourself ( watch a youtube on how to replace ram, it's that easy). Do check how many slots are used/free. If they used up all slots, you need to get the old ram out, put new ram in. If there's slot(s) free, you can ad ram. But, it does work better if you have matched ram. Or , one dimm, or 2 dimms matched pair, or triple or quadruple matched. The latter two not really necessary anymore as we got single dimms of 16 gig now. Maybe even more. Probably only two slots on your laptop anyway. Make sure you match the mem speed with what the laptops motherboard can handle. Mem selling websites for laptops usually have an option where you can fill in your brand and model and let you choose. Be weary they can force you a certain way to make you buy their more expensive ram.
Pick the highest speed SODIMM your laptop mobo can handle, pick the lowest cas timings you're willing to pay. 4 to 8 gig should come somewhere around 40 to 80 bucks.