Upgrade nmap version in source

I am using nmap 7.70 for my project. I want to compile and upgrade nmap 7.8. Please help

This can be done, but there is a substantial learning curve.

You will need to be able to build your own image, using either the imagebuilder and or the full buildroot. This will allow new package binaries to be compiled, even if you don't intend to flash an entirely new image.

Then, once you do that, you will need to understand how package Makefiles are constructed, modify the Makefile and build a new binary of the package. Unless you have some familiarity with programming, at the very least shell scripting, you may find this to be a little complex.

Start looking here: https://openwrt.org/docs/guide-developer/start

There's a lot of documentation to get through.

Nmap package - OpenWrt

It's was updated in March by the maintainer.