upgrade the item for better speed

First: this is an open space, not affiliated to iFixit, where happy customers help other happy customers. Thus, you should thank them, not us.

About your issues, a tablet is not a PC. Thus, expanding it it's a tricky business, and often the logic board is all well soldered.

Your unit is the Tab GT p1000, am I right? If it's that, it has the microSD slot.

One of the things you could to help is getting a fast microSD from a reputable and verifiable source. On my devices, I use Verbatim, Kingstone, Patriot and Sony, for example, and I never got misled.

Another thing that may help, but just a notch because a proper installation of Android is already equipped for that, is using a Task Killer and kill off periodically unwanted apps.

Then, be careful with widgets. To be snazzy and look smart around friends, I used to keep lots of widgets on my no-brand tablet. And I mean, six different iterations of the same clock widget just to know what time is it in Russia, Australia, Japan, Central Europe, New York and Jerusalem, Everynote, LauncherEX appointment manager even if I use a custom legal agenda and stuff.

When I decided to act as a reasonable man, all started to get better.

That's all that I can say about your issue: a more through job looks impossible, or needing a mindboggling level of expertise.