You cannot replace the CPU other than by replacing the entire system board, and there is no board you can use that has a CPU supported by Windows 11.  You need a new system. You can run Windows 11 -- but unsupported by Microsoft.  
I've checked my Inspiron 15 7000 Gaming if it is compatible with Windows 11 and I've got the result, that the CPU "Intel(R) Core(TM) i7-7700HQ" is not compatible. Which CPU could I use? Does somebody has a recommendation of a compatible CPU for my Laptop and perhaps an installation guide?
Change CPU to make Inspiron 15 7000 (7567) Windows 11 compatible