To install the hi-res pack you have to download the hi-rez pack from HTC, install the files on your computer, then start the game. When the first clipboard comes up, you click on "Video". Then you use the drop down box to change from which ever texture size setting you were using to the new 1024 textures.
To stop using them, you start the game, click on the "video", and use the drop down box to change to which ever texture size you want now 512.
As for freezes, check for how many processes you have running ( you kids always have those "chat" things, and music, and porn going all the time
), also check to see how many films you have in your folder. As this file gets bigger and bigger it takes the game longer and longer to find what the next "number" should be which creates freezes when you start a new recording.