When I should submit previous published version(s)? I'm going to send manuscript for publication in IEEE Transactions. Some parts of this manuscript were published earlier in little-known journals (in Russian). But in general manuscript is significantly different from previous papers. Should I upload previous papers as a ‘Previous Published Version(s)’, and upload summary of differences?

UPD:
I found the following in ScholarOne Manuscripts (IEEE Transactions manuscript submission site): "Has any portion of your paper been published elsewhere? If yes, please include your original paper and a brief summary of your changes. New material must be added before submitting the manuscript to this journal.". So, I should upload previous published versions?
While I'm not too familiar with the IEEE publication process, in particular, the common sense tells me the following. Since your manuscript in its present form is "significantly different" from the previous versions, it very well makes sense to simply submit the current version as an original publication. However, it would be nice (and right - in order to prevent self-plagiarism accusations) to mention somewhere in the paper (preferably, in the introduction section) that the present paper is based on previous work by such authors, which has been published in such journals / outlets.

The "previous published version(s)" option that you have mentioned seems to be directed toward more closely related versions of the same paper, which seems to be not the case in your situation.