We’d love to help you optimize your site but that is outside the scope of our support. I can give you just the main tips but every site is individual.
1) Plugins. When you have multiple plugins installed and activated on your site, it can slow it down. So, please, keep enabled only those plugins that you really need for the correct functioning of your site and disable all the plugin that you don’t use. The more plugins you use, the slower it will be.
2) Caching. The most important part of optimizing your site is caching. Combine cached page with gzip compression to get better results. We recommend using W3 Total Cache. Read the beginners guide to setting up W3 Total Cache plugin https://premium.wpmudev.org/blog/w3-total-cache-settings/
3) Images. Use optimized images only otherwise you will have big images and a slow loading time. Do not upload larger images than what is needed. When you use image editing tool like Photoshop don’t save images without using the option “Save For Web”.
There are different ways on how to compress images. Use special services or WordPress plugins to optimize your images for decreased loading times:
– Ewww Image Optimizer
– Smush Image Compression and Optimization plugin
Sometimes slow speed can be a result of your hosting service. If you have checked the above items and the site is still slow, the most likely it is a server/hosting issue. Contact your host and discuss it with them. Because even with default WP theme site speed is slow.