Hi,
Here’s the [https://topics-cdn.dell.com/pdf/inspiron-15-7577-laptop_service-manual_en-us.pdf|service manual] for the laptop, taken from this [https://www.dell.com/support/home/us/en/04/product-support/product/inspiron-15-7577-laptop/docs|webpage].
Go to p.69 to view the necessary pre-requisite steps and then the procedure to remove/replace the heat sink.
Once the heat sink is removed there is access to the CPU and GPU