If you have the white NOW TV box or the purple Roku streaming stick then you will have to buy something more up to date.
I have both of those and they are both unusable now. This is because they have a slow processor in them that can't cope with modern apps.
I recently bought a Roku Express, which was released in Autumn 2017 I think, and it works great as it has a much faster processor. It is quite cheap to buy on Amazon.
I've been having same issues with mine and initially thought it was a remote problem. I have a stick and probably only purchased maybe a year ago at the most. It has become so unresponsive. It's as though it takes 4 or 5 mins for it to catch up. Once you eventually get to your selection watching programmes isnt an issue. I've tried updates, unplugging from tv for 5 mins. It's pretty much become unusable and I'm annoyed I'm paying for something I cannot watch.
While it’s plugged in, hold in the little reset button on the side for 15-30 seconds, and when it wakes up, set it up again.
This can get rid of a lot of cruft.