Hi,
Here is a link to the [https://download.lenovo.com/consumer/mobiles_pub/ideapad_300-14isk_300-15isk_300-17isk_hmm_201610.pdf|service manual] for your IdeaPad.
Scroll to p.55 to view the necessary pre-requisite steps and then the procedure to remove the fan/heatsink assembly.
Scroll to p.87 to view the parts numbers (#12&13) for the fan and heat sink. Search online using the appropriate ''part number only'' to find suppliers of the part that suit you.