First impression...
Easy as pie, I found. I made a copy of my RPGMV folder, then triggered the Update that I'd downloaded. Finished in a few minutes, no problem. I then extracted from the NewData folder the index file, and the js folder.
I chose one of my numerous Projects, made a copy as a precaution, then replaced the index file, and copied over the js files, all except the plugins.js file. I'm using Windows 10, which is intelligent enough to over-write a folder's contents, rather than crush the folder and replace, so it was very simple. No issues.
Now for the test... I had been using the O-ggy Memory Patch Plug-in to control memory leakage, but this Update should make that redundant. I launched Project, then, and removed that Plug-in. I then tested the Game, watching for memory leakage, and I'm pleased to say that there was none..! I could artificially push the memory usage up to over 2 Gb, by hammering the Menu On-Off, but once normal play resumed, the memory dropped back to very reasonable levels. Not immediately, as the System seems to recover unused memory every few minutes, rather than 'real time'. In normal play, changing Maps, and evoking the Menu, memory was held in check admirably. Result..!
The other issue I had with 1.3.1 was the scrolling text which no longer worked. That, too, has been fixed in this update.
I updated a couple more of my Projects, with the same success; I'm very pleased.
Result for the moment is a firm 'Thumbs up..!' from me. The usual precautions of course, such as making a copy of one's whole Project before updating, and with the proviso that I use very few Plug-ins, so cannot affirm that they will all cooperate with this version; other than that, it's fixed the only issues I had with MV. Here's hoping it gives as good a result for everyone.