Very hard compared to other engine swaps.
3.0l and 4.0l are not related so transmission will need to be changed, so maybe drive shafts as well
In any engine swap you have to change computer and wiring harness, and since your year also has PATS(anti-theft system) you would need to get a dealer or lock smith to add existing keys to new computer, if it had PATS too.
All in all it depends on what you have now and what you want as the end result.
If current 3.0l Ranger is in good condition, money is better spent selling that one and buying a 4.0l Ranger.
It 3.0l Ranger has a failing engine then a rebuild or used 3.0l engine would be best bet
And just FYI vehicles without stock engine size, even if it's an improvement, are worth less money because they are a pain to work on, often parts won't match when you want to replace alternator or water pump, even spark plugs, lol, unless you know the year of the Engine