How can I scan slides to digital, and upload them to dotphoto?

Your best choice depends on how many slides you want to scan.

Up to 5 slides for dotphoto Club or other Annual Accounts

If you have a dotphoto Club or other paid account, dotphoto will scan up to five slides and upload the digital images to your account as part of your annual plan. If you would like your slides returned, please include a self-addressed, stamped envelope when you send your slides to:

dotphoto Club Scanning

Box 92

Titusville, NJ  08560

Include your name, phone and dotphoto login.

100 Slides

The Kodak Scanza is a handy device for converting slides to digital. It's slow, but, if you have the time, it's a nice tool. We use the Kodak Scanza at dotphoto. About $150 at Amazon. https://www.amazon.com/KODAK-SCANZA-Digital-Slide-Scanner/dp/B00O2BU8PK/ref=sr_1_2_sspa

200+ Slides

One inexpensive solution: set up your camera phone on a tripod in a dark room. Set up your slide carousel, and photograph your slides. You'll get pretty good resolution and review your slides at the same time. Try a few first to ensure that you like the quality. 

Or choose one of the online services that specialize in bulk slide scanning.

ScanCafe charges 48 cents per slide plus the transfer medium, so 200 slides would be $96 plus $10 for the download.

https://www.scancafe.com/services/slide-scanning

Homemoviedepot will scan a box full of slides, 8mm movies, VHS, and just about anything you've got for a flat rate of $349 plus shipping. You can fill a medium UPS Medium Express or FedEx Medium box with materials, up to the limits specified, and they will transfer all of it to DVDs. https://www.homemoviedepot.com/easy_box.html

Note that Homemoviedepot only accepts 35mm slides and that you are limited to 750 images per box. That means your cost per slide is $349 / 750 or 46.53 cents per slide -- just slightly less than ScanCafe, so, unless you need exactly 750 slides or a mix of media, you're better off scanning slides at ScanCafe.