First, agree on access
Ask the owner for a project invitation and the role you need. Owners and editors can upload revisions. Viewers can inspect and download, but cannot publish changes. Contributors can submit proposals when the project's Review setting is enabled; with Review off they have viewer access.
Pro project owners can enable Review so every new upload, including the owner's, becomes a proposal. An owner or editor approves it before publication. This is different from sending an external visual review link: a reviewer's decision on that link does not publish a project revision.
1. Start from the right revision
Open the Project's Versions section. Select the revision you want to build on and download its originals from Original files. Read the editor and license metadata before editing. Use your own CAD application to make the change; STL Diff is not an in-browser CAD editor.
Keep a short note of what you changed and why. Export the updated preview mesh and matching originals, or use a STEP as the main upload if the owner enabled automatic STEP to STL conversion.
2. Upload the next version
Choose Upload Revision, or Submit for Review when project review is enabled. Drop or browse for one or more models. Select each queued file to edit its name, comment and matching source attachments. Files follow modification dates; after direct upload you can reorder revisions. Editor and reuse terms apply to the entire upload. Uploading a new revision preserves the previous model and its originals. You cannot replace originals on an already published revision.
With Review enabled, the upload waits in the project's Reviews section. The owner or an editor can inspect it and request changes or approve it. For another round, upload the updated model and its originals together. Earlier rounds retain their own files; approval publishes the accepted package as the next revision.
3. Compare geometry and share the review
In Versions, assign an earlier revision to A and the new one to B. Changes shows the difference in that direction. Swap A/B if needed. The inspector follows B; Model shows that single revision, and Changes compares it with the selected base. Search, Pair and Originals filters help you find versions without changing the saved history.
Inspect added and removed regions in the viewer. Use the alignment and display controls to choose a useful view: automatic alignment can hide a deliberate move, while no alignment preserves the original coordinates. Mesh comparison approximates geometry; it is not a comparison of CAD feature trees.
Use Share for review to create an interactive link. Recipients can inspect it without an account. Review-link limits and lifetimes depend on the sender's plan. Source access is separate: a visual review link does not include your editable CAD files.
4. Keep the next person in the loop
Keep the accepted model, its originals and a useful revision name together. Pro owners can separately enable project email notifications; those updates follow the project's setting. For manufacturing or printing, download the intended revision and verify its dimensions, geometry and suitability in your own tools.