Since it has two RAM slots (very rare in ultrabooks!), you can easily add another 4GB to make it 8GB dual channel, or get 2x8GB for 16GB total. RAM type is DDR4-2133 SODIMM. 4GB DDR4 costs about $30 so it's actually cheaper than the previous deals.
How to remove the base cover: https://support.lenovo.com/au/en/documents/pd104237
Memory module installation: https://support.lenovo.com/au/en/products/Laptops-and-netboo...
Don't forget 7.5% Cashrewards.