CSS changes wont work

Any CCS change i make wont take effect on my WP site. I have no idea why this is happening, im new to wordpress but ive been trying to find an answer everywhere and there is none.

PD i already tried the control+F5, just doesnt work.

My theme is Alyeska from Theme Boulevard, and what im trying to do is change the size of my headings in the post grid. More specificly im trying to change the font size of the h2, although none will change. I also tried changing the h1-h6 for the whole site. Anyway this are the code (both stays the same even after i change the font_size parameter):

/* =Post Grid
----------------------------------------------- */

.post_grid .grid-row {
	margin-bottom: 30px;
}
.post_grid .grid-row:last-of-type {
	margin-bottom: 0;
}
.post_grid .entry-title {
	font-size: 20px;
}
.post_grid .article-wrap {
	padding: 0;
}
.post_grid article {
	background: transparent;
	border: none;
	padding: 0;
}
.post_grid .entry-content {
	padding: 0 5px;
}
.post_grid .header-shade {
	display: none;
}
.post_grid .excerpt {
	font-size: .916em;
}

/* Headings */
h1, h2, h3, h4, h5, h6 {
	font-weight: normal;
	margin: 0 0 12px 0;
}
h1 {
	font-size: 32px;
	letter-spacing: 1px;
	line-height: 1.15em;
}
h2 {
	font-size: 23px;
	letter-spacing: 1px;
	line-height: 1.15em;
}
h3 {
	font-size: 1.5em;
	line-height: 1.15em;
}
h4 {
	font-size: 1.25em;
	line-height: 1.15em;
}
h5 {
	font-size: 1em;
	line-height: 1.6em;
}
h6 {
	font-size: .75em;
	line-height: 1.6em;
}
hr {
	background-color: #cccccc;
	border: 0;
	height: 1px;
	margin-bottom: 1.625em;