How to upgrade windows 7 to windows 10 on a Toshiba R705-35 laptop?

You'd buy a license and start setup - it will normally just upgrade and keep apps, data and settings. Missing drivers will be found through windows update automatically (I cannot even remember a single machine where this hasn't worked and I have upgraded over 100).

However, this is an 11 year old device, I would not recommend this. Win10 needs more resources than 7 and I can imagine this machine won't be very fast even on 7 at the moment.

I know its old but I installed an SSD drive and upgrade memory from 4G to 8G and on windows 7 it runs pretty fast, I want to put in use for basic operations such as MS office and internet browsing. 

When you can install an SSD and more RAM, then I would give it a try, but then it's not simple OS upgrading anymore ;)

I second @McKnife. From my own experience on "comparable" devices manufactured from 2011 to 2013:

Some applications may be usable, but a fun-limiting factor is the GPU. You won't be able to run any fancy stuff. This includes also some modern HTML5/WebGL based web-sites. Graphics operations requiring modern shaders will run terribly slow, when they are able to run at all.

[..] use for basic operations such as MS office and internet browsing.

As home means Microsoft 365 nowadays, I would install Ubuntu and run Office in the browser.
Mandatory components like Cortana and co will eat much of that performance.

"I want to put in use for basic operations such as MS office and internet browsing" - ok with an SSD, it will do ok for those basic things.
About the license: there have been heavy debates going on whether you may upgrade for free or not. Technically, it works, but MS has never explicitly said that the upgrade remained free after the 1st-year-free-upgrade period.

As was suggested, get the upgrade advisor and run it, make sure to uncheck apply updates while going through the process.

Depending on what you have installed, sometimes the newer win10 versions had issued with certain components. If this is what happens in your case, locating an older version of Windows 10 tool 18xx might prove useful to then upgrade to the current version.

Make sure to have a backup, image before starting..

In this situation I'd erase the drive and install W10 from scratch.  That's based on the number of "issues" I've seen here over the past year installing W10 over W7 as an upgrade.  

If the version of W7 on the system in question is 32-bit then you'll have to install 64-bit W10 from scratch.

Agree with Dr,klahn to a point, the question with install from scratch deals with whether the win10 license from a prior upgrade attempt attached.

With branded you may still have to go win7 to win10 upgrade route even if 32bit to confirm the win10 digital license is there to activate, after which you can reinstall win10 64 bit from scratch.

Do not remember where, but I saw that there was a repository linked to the different creation media tools of different prior version,  get it a 2018 18xx version should be a smooth upgrade process. I think the 19xx had some issues with Intel storage controllers.

i think this can help :  https://www.tenforums.com/tutorials/139745-upgrade-windows-10-windows-7-free.html           UPGRADE