… Well, than have fun 
Even if you use your old, well thoght you local disc structure - images will disapear.
Easy solution, just upload again, but you must change data name - old fashion desaster (remove or refresh will not do)
More tricky - often 2.6.1 will not show the exact position.
Only workaround - delete row and build content new.
Happens often, so be aware…
…there is no such thing as convertning anything from former 2.xy versions to current 2.6.1.
Internal classes have obviously changed without prior notice (can say that as blocs news are first each day)
Have a special look at your lightbox galleries.
If you have done somework via classes in submenue on your arrows,
don´t get nuts, a simple workarround can solve, but it will stil be a different look as the standard is now obviously light unless you hover.
An added png or gif can easily restored by clicking the colour and change it once by clicking class section “done”.
You need to do it for both - “previous” and “next”
Once done it seems ok for the project.
Missing images is a bit more anoying as rows and positions are not properly shown.
REBUILDING seems to be neccessary - Holy moly if you have a bigger project.
Personally happy up to 2.4.5, than trying 2.5-all versions, but knowing now better.
Rebuilt is a must.
So, instead of doing this know - let´s see how 3.xy will cope with hours and days of our work - and trust - with projects we all did with a 2.xy version.
Still hopefull, but there is bootstrap 4 and so - better be prepaired to rebuild the whole lot.
Happy bloc´ng