How to install 240GB SSD

@huud yes you can, just not a 240GB (does not exist:-). The X510 series uses M.2 SATA SSD across that series. In addition the X510QA uses M.2 NVMe™ PCIe® 3.0 SSD. Storage is from 256GB to 1TB. All of them also have expansion slots from M.2 2280 PCIe 3.0x2 and M.2 2280 SATA3.

For the how-to, check something like this video While you work on your Asus Laptop, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has a device with the same issues as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Repair is War on Entropy!