Do you have a link to the laptop? That alone doesn't tell me what I need to know about it.
Here's a new one: https://www.amazon.co.uk/Acer-Extensa-i5-7200U-256GB-Windows/dp/B07F3H1P68/ref=sr_1_1?s=computers&ie=UTF8&qid=1548281667&sr=1-1&refinements=p_72:419153031,p_36:-50000,p_n_feature_fifteen_browse-bin:8322530031|8322531031,p_n_feature_browse-bin:1481781031,p_n_condition-type:12319067031
Refurbished: https://www.amazon.co.uk/Lenovo-Ideapad-320S-14IKB-FHD-14inch/dp/B07H4VJNBQ/ref=sr_1_5?s=computers&ie=UTF8&qid=1548281775&sr=1-5&refinements=p_72:419153031,p_36:35000-50000,p_n_feature_browse-bin:1481781031,p_n_feature_fifteen_browse-bin:8322530031|8322531031
If I get a ddr3 is that okay or should I get a ddr4That should be fine.