Hi @shauryaanand
Here's the [https://dl.dell.com/manuals/all-products/esuprt_laptop/esuprt_inspiron_laptop/inspiron-15-5559-laptop_service%20manual_en-us.pdf|service manual] for the laptop series.
Go to p.56 to view the procedure to remove the ''heat sink assembly.''
Once it has been removed you can refresh the thermal paste on the CPU.
Here's the ifixit [guide|744] guide that may also help.