Improve Creloaded / OScommerce website load time and optimisation

We need to improve the speed our website loads on our dedicated server. We have performed some server optimisation but the website still takes over 15 seconds to load. Following discussion with our host they have provided this suggested list of improvements which could be made. Could you please let me know if you are able to implement these fixes and speed up our website. Please contact us if you need further information. Thanks RECOMMENDATION GRADE TYPE PRIORITY Combine images using CSS sprites F (0) 71% Images Medium Serve resources from a consistent URL E (52) 94% Content High Avoid landing page redirects C (76) 97% Server High Optimize images B (84) 74% Images High Prefer asynchronous resources B (85) 93% JS Medium Minify CSS B (87) 84% CSS High Leverage browser caching A (90) 61% Server High Specify a character set early A (95) 98% Content High Minify JavaScript A (97) 91% JS High Serve scaled images A (98) 85% Images High Minify HTML A (99) 94% Content High Avoid bad requests A (100) 97% Content High Avoid a character set in the meta tag A (100) 95% Content High Defer parsing of JavaScript A (100) 67% JS High Enable gzip compression A (100) 83% Server High Enable Keep-Alive A (100) 96% Server High Inline small CSS A (100) 93% CSS High Inline small JavaScript A (100) 97% JS High Minimize redirects A (100) 93% Content High Minimize request size A (100) 99% Content High Optimize the order of styles and scripts A (100) 94% CSS/JS High Put CSS in the document head A (100) 100% CSS High Remove query strings from static resources A (100) 89% Content High Specify a cache validator A (100) 94% Server High Specify a Vary: Accept-Encoding header A (100) 90% Server High Specify image dimensions A (100) 52% Images High Avoid CSS @import A (100) 96% CSS Medium