^

While WD40 is okay on freeing seized or rusted up threads, too much of it will contaminate your sparkplug threads. Thus leading you to over tightening the new plugs (because madulas eh from all that WD40 leftover).

Try to use it sparingly, (the little red pipe is there for that).

You can use a short extension (iron pipe, etc. what's available) to give you more leverage.

Or, take it to a mechanic, and observe what he does. Para second time around, you know what to do.

Goodluck.