Imagery and resizing

I added a couple of my photos to a new site and they are about 8MB and thus a bit large. There was no restriction until I tried to upload to the test site, fortunately I have a server to test on, but anyway the question.
What is the best image editor available for making these pics a whole lot less large; I already use Irfanview which is great but I need to make the images a sensible size for a responsive web site. Any help welcome, as I don’t really know what I am doing.
Here is a rather large site because of two images which are lovely but a bit too big.
https://flowerborder.co.uk/
Kevan

You can do this directly in BSS

When you import/drag the images it will ask if you want to optimise.

For images already in your design, right click in the images and choose optimize

image

You can then change the width and height along with the file type (jpg, webp or png) and quality:

Thanks, I did optimise and alter the width on one of the original images. The exported files I then used were about 8MB in both cases. I have downsized to a smaller image in Irfanview, but this will not fix the issue of being a huge download file for a phone and does not offer the option of using srcset with different sized files, which is a shame. Worth the £20 for the software, though, and I would still recommend it, and will play a lot more to get something half decent, as I have all of my sites using bootstrap but not properly.
Kevan

I’m not seeing any massive images on your website, but there are plenty of websites out there that allow you to upload and optimize images for size and quality. Here’s one that is totally free…

Good answers from both richards & printninja.
I sometimes use https://convertio.co

If you want to buy software the Affinity products are pretty well priced.