Investment PPT Theme/UI/ Graphic overhaul

My company is an event management software company that uses mobile payments and data analytics to manage events.We are raising a seed round and need to redo our investment deck design/UI/aesthetics.We have an old deck that looks good but we need add/edit slides from it.We are looking for good slide design and graphic design that will make our deck look seamless frok page-to-page,as well as of high quality.
The deck is 12-18 slides long(with 2-4 appendix slides