I would like to know how I can change file limits in a document library.
The clear cut answer is:
No, You cannot change the limit of Threshold in SharePoint Online.
Already answer this here.
You can handle your large list using Manage large lists and libraries in Office 365.
For your more information you can visit
- Office 365 : How SharePoint Online handles List View Threshold
- The number of items in this list exceeds the list view threshold
What you can do is divide your files in folders in document library.