How can I download my photos of my IPhone to a folder on my desktop. It's telling me I only have 1 photo on my IPhone which is wrong. I can't even install a new update IOS 15 on my IPhone

Can't download pictures from my IPHONE to a folder on my desktop?

See this Apple article: Transfer photos and videos from your iPhone, iPad, or iPod touch

Transfer photos and videos from your iPhone, iPad, or iPod touch to your Mac or PC - Apple Support

I also can't install IOS 15 on my IPHONE.

You need about 7 GB device storage, to free up iPhone device storage see this Apple articles below:

If you need more space for an update on your iPhone, iPad, or iPod touch

If you need more space for an update on your iPhone, iPad, or iPod touch - Apple Support

How to check the storage on your iPhone, iPad and iPod touch

How to check the storage on your iPhone, iPad and iPod touch – Apple Support (UK)

Clear Other storage on your iPhone or iPad

Clear Other storage on your iPhone or iPad - Apple Support

What's the difference between device storage and iCloud storage?

What's the difference between device storage and iCloud storage? - Apple Support

See also the following Apple articles:

Update your iPhone, iPad, or iPod touch

Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If your iPhone, iPad or iPod touch won’t update

If your iPhone, iPad or iPod touch won’t update - Apple Support

If they are On, turn Off Hotspot & VPN.