2 problems with your inquiry. You have a 6th gen CPU and cannot upgrade to an 8th gen CPU (which is the minimum CPU requirement). The other problem is that the 3459 is not on the Dell compatible list for Windows 11. Which means if you do install Windows 11 on a non-compatible system and require tech support, Dell tech support will insist that you install Windows 10 before they will offer assistance. Also though you probably could install Windows 11 anyway, you have an unsupported system. So MS has stated that they will eventually stop any updates on those systems. When it may happen and which updates no one seems to know.  You have a system that is around 6 years old and are running a very stable OS in Windows 10. Windows 10 will be supported for 4 more years and it may be worth waiting for a few years and then upgrading to a new compatible Windows 11 system (assuming another version of Windows is not around). I said assuming because Windows 10 was supposed to be the last Windows version and my crystal ball broke long ago.
In considering upgrade to Windows 11, my 3459 does not meet specs for CPU. Is the 3459 able to upgrade easily and if so, what CPU's would be compatible with 3459 and Windows 11?  I searched but did not see that anyone asked this question for the 3459.   Thank you. 
3459 AIO Inspiron CPU upgrade