How to install iOS 14 in iPhone 5s

You can't.

iPhone 4S has a 32bit chip with 512MB RAM.

iOS 13 and higher requires 2GB RAM or more and a 64bit platform. iPhone 6/6+/5s has 1GB RAM

These are the iOS options based on iPhone Model --> You need to Identify your iPhone model - Apple Support

• iOS 15.2 —> 6S / 6S Plus, SE (1st Gen and 2nd Gen), 7 / 7 Plus, 8 / 8 Plus, X, XR, XS /XS Max, 11,11 Pro /11 Pro Max, iPhone 12, 12 Mini, 12 Pro, 12 Pro max, iPhone 13, 13 Mini, 13 Pro, 13 Pro Max
• iOS 12.5.5 —> Final release supported on iPhone 5S, iPhone 6/6 Plus, 

Learn how to--> Update your iPhone, iPad, or iPod touch - Apple Support

There is no method to install iOS 14 on an iPhone 5s. The last version of iOS that it can support is 12.5.4

You cannot on iPhone 6, only to 12.

How can I upgrade my iPhone 6 to iOS 14