Is there a specific size I need to upload for the photo gallery. Usually I have photos in the range of 10MB. If I do so will the site reduce the Size?
This is an answer from a ‘non techo’ but long time user of Concrete and similar CMS.
I would suggest that you check the size of the image that gets displayed on your system or similar. From memory the largest shown on screen is about 1200 pix wide. So if your image is 10MB you are gobbling up the space on the server storing it but not actually using that resolution on the screen. The actual photo size on screen in pix will be shown if you choose the format photo tab.
On our Concrete CMS site (V9) I have uploaded a photo banner headline of 5.3Mb (.PNG format) and could not understand why it was so slow loading. Converting the pic to .JPG reduced the size to 280k and it now loads very fast. Obviously if you have superfast broadband you might get away with bigger photos, but here in West Wales we don’t.
For the non Concrete website I support, our Webmaster has suggested that pictures should be set to about 500k before being uploaded. I use the free app PIXresizer to reduce images to around that sort of size. They look great on the site. The only problem is where Members send us stuff as photos embedded in their iPad email. These photos when extracted tend to be around 20-30k which means we have keep them very small if we want to use them. My ‘rule of themb’ for Members sending us photos is to send them as attachments and to have a minimum size of about 1500k. That allows us to clip them to enhance the image if necessary.
Hope that helps
Regards
Pete
Today’s cell phones (which most people are using to take pictures these days) have many megapixel defaults. The resulting images can be huge, and would not fit any monitor without being shrunk for display. Good for printing wall-sized posters though 
If you are the one uploading, I highly recommend this free program for Windows users: FastStone Image Viewer - Powerful and Intuitive Photo Viewer, Editor and Batch Converter
It can convert/resize/crop very quickly and can also do so in batches (also has a nice slideshow and thumbnail viewer).
For concrete CMS, be sure to set reasonable quality, compression, max width, and max height settings in:
Dashboard > System > Files > Image Uploading:
https://yoursite.com/index.php/dashboard/system/files/image_uploading
This will keep the file sizes kept on your server sane, and can save a huge amount of disk space.
Also, be sure to check the sizes/settings at:
Dashboard > System > Files > Thumbnails
For example, say you uploaded a file that was 4000px wide and had a max width setting of 2000px, and a large image thumbnail set at 1140px.
This will save several variations of the file in the File Manager: 2000px resized, 1140px large, medium, small and tiny thumbnails (or any others you may have added). The 4000px uploaded image is not saved.
On a 1200px wide monitor/browser, you would see the 1140px on the front end of the site. The 2000px “original” could be used as a download.
Now, if you upload a 16000px image, you may find uploads not only take a long time, but so would the conversions (and possibly hit a PHP timeout).
Hey, Yitschok you can get the all detail from the official doc. It is possible but but it will take more space so better to use any online application such as https://jpegcompressor.com/. For compressing you image, it will compress images without losing quality.