There are few ways:
- Via TinyPNG WordPress Plugin which you can manage your photos directly within your WordPress Dashboard
- Pre-optimize your images before you upload via TinyPNG/TinyJPEG Website
- If you are on Windows, you can use a downloadable tool RIOT(Radical Image Optimization Tool) to pre-optimize your image before you even upload them reducing unnecessary bandwidth to your hosting.
I personally use RIOT first then check if I can still reduce it on TinyPNG, and when I am satisfied, I then upload it to the site. RIOT can bulk optimize an entire folder of images so it's easier and faster.