Can I change gpu in insprion laptop. I don't know why it has only intel uhd family graphics can I install nvidia gpu in it

It's very unlikely that you can.  Although this thread was posted in Inspiron desktops forum, your indication of a laptop suggests that you may have an Inspiron 15 3530 or Inspiron 15 3535.

With either models, the discrete graphics option is NVIDIA GeForce MX550 2GB GDDR6 and it's only available at purchase configurations.  To upgrade video card on your laptop, you must replace the whole motherboard.