Such an open ended question how long is a piece of string.
Step 1. Remove the table then stretch a string between the the top wheel and the bottom with the string just touching the top wheel top and bottom it should align with the lower wheel at the same time top and bottom. Having removed the guides top and bottom at the same time as the table. Check there is not play in the two main wheels. Alignment is critical. Tension guides must run true.
I would modify the throat pins by opening the gap to allow two bearings in place of the pins often you can buy after market guides and modify these to fit your saw. Replace the rearbearing that prevents the blade being pushed back from the vertical set it with a small clearance ensure it is right angles to the blade.
Never adjust the side guides unless you can turn the saw wheels around by hand to ensure they are seated best on the blade.
Sorry was about to write a manual for bandsaws but I do believe there are excellent books, videos etc devoted to the bandsaw.
About now its time to narrow down from United Kingdom addy you may find a wood group near you they have libraries your local library may have a craft / woodwork section. There is no magic bullet just patient alignment. One of the worlds best operators bandsaw was average in manufacture but cut thousands of disks for bowls etc but was properly aligned.
Anyway starting from the beginning straightedge the wheels long steel rule is cheap and effective just imagine a car out of alignment . Look for someone who is familiar with bandsaws never give up Jim. I have bought several books on bandsaws never regretted the money spent on them.
Peter.
