It's possible. A lot of dust can accumulate in a laptop, especially in the fan and the heat fins, impairing their cooling performance. The thermal paste tends to dry out over time and become less effective.

While you are inside the laptop, you might as well replace the CMOS battery, as they are cheap.

You'll need to completely remove the old thermal paste before applying fresh. For new thermal paste, Arctic MX-4 is a good choice. It's non-metallic (unlike Arctic Silver and many others), so if you accidently get a bit on another component, it won't be a disaster.

Whenever touching components or working inside a computer, wear a grounded wrist strap, also called anti-static wrist strap, ESD wrist strap, or ground bracelet. I know many people do such work without this, but it's a cheap and sensible precaution. Rest the laptop on an anti-static mat or at least a reasonable alternative such as corrugated cardboard.

Follow the disassembly and reassembly steps in Dell's Service Manual:
https://www.dell.com/support/home/en-us/product-support/product/xps-15-9550-laptop/docs
Look on YouTube for videos showing disassembly of your model. But, be cautious with them, as some use steps or methods that are not appropriate. Use the videos to add to your understanding of what to do, but follow the steps in Dell's manual.

In addition to a grounding strap, you'll need fine screwdrivers, plastic pry tools (spudgers/scribes), and maybe tweezers or small magnet to remove loosened screws that you can't get out of the receptacle. Local computer stores, Amazon and AliExpress sell small kits of tools specifically for computer disassembly.

Keep organized. As you remove screws, make sure you know where they go since not all are the same size. I use trays from chocolate boxes with many small compartments, to organize my screws. I put a piece of tape in each with a number, and I write that number on a piece of paper noting where those screws or parts came from.

Follow the disassembly and reassembly steps in Dell's Service Manual:
https://www.dell.com/support/manuals/en-ca/g-series-15-7588-laptop/g7-7588-servicemanual/before-working-inside-your-computer?guid=guid-5d3b1051-9384-409a-8d5b-9b53bd496de8&lang=en-us
Look on YouTube for videos showing disassembly of your model. But, be cautious with them, as some use steps or methods that are not appropriate. Use the videos to add to your understanding of what to do, but follow the steps in Dell's manual.

To clean off old thermal compound, Arctic makes an excellent product. For Canadian $10 I got a package containing a bottle of ArctiClean 1 and a bottle of ArctiClean 2, enough to do several computers. ArctiClean 1 emulsifies old paste. ArctiClean 2 purifies the surface, removing any cleaner residue.
http://www.arcticsilver.com/PDF/appinstruct/ac/ins_arcticlean.pdf
https://www.overclockers.com/arcticlean-review/
https://www.techpowerup.com/review/arctic-silver-arcticlean/2.html
To remove old thermal compound, you could instead use high-purity (over 90%) isopropyl alcohol. But, ArctiClean's kit works so well and is inexpensive, so go with that.

When removing old thermal compound, be careful not to let any bits fall onto board or components. If it's metallic, those stray bits could cause problems later.

Many recommend coffee filters for cleaning, but many types of coffee filters have varying amounts of lint. Ideally, you want a lint-free material, such as microfiber cloth.

As I wrote earlier, Arctic MX-4 would be a good thermal compound choice for a beginner, as it's non-metallic. Check what application method Arctic recommends for your processor:
http://www.arcticsilver.com/intel_application_method.html#

Depending upon how dirty the inside of the fan is, you may be able to clean it just with a can of compressed air and a brush, or you may want to disassemble it. The old Inspiron I recently opened had so much dirt and fluff in the fan and heat fins that it was best to disassemble the fan, thoroughly clean it and then reassemble it and seal the joints exactly as it was from the factory.

Taking apart and reassembling a laptop is not easy and you could damage a connector if you're not sure how to open it. It's not rocket science, but you do need to be careful and take your time. If you're not comfortable, you could go to a reputable local repair shop. Good luck.