How to Decrease the Slideshow module height ?

You can add a max-height value to your custom.css

.owl-carousel .owl-stage-outer {
max-height:500px!important;   <---Change the px value as per your needs 
}

If you do not have a custom.css file then you can create a new one in this folder /templates/ja_playschool/css/

Hope it helps

how about moving the title and button up to the center?

You can add a negative margin

.acm-slideshow .owl-carousel .item .slider-content-inner {
margin-top:-200px;
}

Regards