One of the wheels, most usually the top wheel, has a "relaxer" screw ( or the equivalent) which, when turned, pulls the wheels closer together, so you can remove the blade. You will need to take the guides apart (or even off) to do this. The reverse is true also, once the new blade is on, you will turn the adjuster ( screw?) the other way to tighten it. The proper adjustment will be sometimes indicated by the amount of "flex" a blade will do when tight. God bless your efforts.
Answers & Comments
One of the wheels, most usually the top wheel, has a "relaxer" screw ( or the equivalent) which, when turned, pulls the wheels closer together, so you can remove the blade.
You will need to take the guides apart (or even off) to do this.
The reverse is true also, once the new blade is on, you will turn the adjuster ( screw?) the other way to tighten it.
The proper adjustment will be sometimes indicated by the amount of "flex" a blade will do when tight.
God bless your efforts.