Hi @sicko ,
Here’s the [https://download.lenovo.com/consumer/mobiles_pub/lenovo_g_z_50_series_hmm.pdf|hardware maintenance manual] for the laptop.
Go to p.37 to view the necessary pre-requisite steps and then the procedure to remove the HDD so that it can be replaced by a SSD.
If you don’t use the dvd drive (ODD) an option to consider is to remove the ODD and insert the original HDD in a [https://www.amazon.com/Generic-Lenovo-IdeaPad-G50-30-G50-45/dp/B01CTNTCQS|caddy - supplier example only] in the ODD drive bay and configure it as a storage drive, with the SSD as the OS drive. See p.36 for how to remove the ODD.
On p.41 it shows how to remove the memory (RAM).
Here’s a link to just one [https://www.crucial.com/compatible-upgrade-for/lenovo/lenovo-g50-70|supplier - example only] that shows what SSD and ram modules are compatible with your laptop.