As stated you cannot increase the size of a
.jpeg without loosing quality but there is a margin of tolerance that you can increase the size of a
.jpeg before it is noticeable.
Take my hero for instance (original file):
If I import this image into Photoshop and go to
Image > Image Size (Shortcut Ctrl+Alt+I for PC.)
You can change the percentage to 110% and repeat this till you receive a notable difference in quality. NOTE IF the image is high quality you can usually do an increase no more than 10 times from experience but as stated, this depends on the quality of the image you are adjusting.