Thanks for your question.

I agree with you that things can get confusing if you use the internet to get information about pruning lilacs. There are two reasons for this.

(1) Are you pruning your lilacs to reduce their size and/or height?

(2) The way you prune will depend upon the condition of your lilacs before you start your pruning.

Because individual gardeners may answer these questions differently, various approaches to pruning have developed.

You said that that your lilacs are about 14 feet tall. I assume, therefore, that your lilacs have not been recently pruned and that your lilacs were planted many years ago. I would further guess that now you are mainly getting flowers on the top branches and the lower regions of the lilacs have relatively few flowers. For this reason I suspect that you may want to reduce the heights of your lilacs and have flowers appearing over a larger portion of them. I would suggest the following:

(1). Cut out now (late May 2021) any branches which are not developing leaves; they are dead.

(2)). After existing blossoms turn brown, prune the tops of the lilacs to the desired heights.

(3). Very early in spring 2022 remove about 1/3 of the branches down to approximately 8 inches from the ground. This sounds severe and it is. Your lilac bushes will look rather sparse. What you trying to do is to stimulate new lilac branches to grow from the base during the 2022 season.

(4). During 2022, repeat the above three steps. Also during 2023, repeat these same three steps.

The above steps are called rejuvenation/renewal pruning. By the end of 2023, you will have created essentially a new lilac bush. This new bush will be shorter than what you now have, it will be more compact, and it will develop flowers over most of its growth. See the following for further information.

https://hortnews.extension.iastate.edu/1993/2-10-1993/lilac.html - :~:text=Begin the procedure by removing,and remove all the others.

https://www.gardeningknowhow.com/ornamental/shrubs/lilac/pruning-lilac-bushes-when-to-trim-lilac-bushes.htm

https://espacepourlavie.ca/en/pruning-lilacs

https://extension.umn.edu/trees-and-shrubs/lilacs - pruning-1923160

Good luck and please get back to us with any additional questions.