<!-- Resize to 500 pixels width -->
@Html.Sitecore().Field("Field Name Here", new { width = 500, crop = false })
 
<!-- Resize to 500 pixels height -->
@Html.Sitecore().Field("Field Name Here", new { height = 500, crop = false })
 
<!-- Resize to 500x500 pixels with cropping -->
@Html.Sitecore().Field("Field Name Here", new { width = 500, height = 500, crop = false })